Sulfonamide, phenolate, and directing ligand-free indium initiators for the ring-opening polymerization of rac-lactide

Article abstract of DOI:10.1021/om101166s

Reaction of In(CH₂SiMe₃)₃ with H ₂N₂^TsN^py or H₂N ₂^TsN^OMe gave the five-coordinate indium alkyls In(N₂^TsN^py)(CH₂SiMe₃) (14) and In(N₂^TsN^OMe)(CH₂SiMe ₃) (15). The corresponding reaction with H₂N ₂^TsN^Ph gave four-coordinate In(N ₂^TsN^Ph)(CH₂SiMe₃) (16). Reaction of H₂N₂^TsN^py with In{N(SiMe₃)₂}₃ gave the amide In(N ₂^TsN^py){N(SiMe₃)₂} (19). Reaction of Na₂N₂^TsN^py with InCl₃ in THF followed by LiOⁱPr gave the "ate" product In(N₂^TsN^py)(OⁱPr)Cl{Li(THF)} (21). The chloride complex In(N₂^TsN^py)Cl(py) (22) was also isolated. Reaction of In(CH₂SiMe₃) ₃ with H₂O₂^MeN^py gave the bis(phenolate)amine compound In(O₂^MeN^py) (CH₂SiMe₃) (23), and reaction with ⁱPrOH or Me₂NCH₂CH₂OH gave the mixed alkyl-alkoxides In(CH₂SiMe₃)₂(OⁱPr) (17) and In(CH₂SiMe₃)₂(OCH₂CH ₂NMe₂) (18), which are dimeric in the solid state. The X-ray structures of 14, 15, 17-19, and 21 - 23 have been determined. The compounds were evaluated as initiators for the ring-opening polymerization of rac-lactide. With the alkyl and amide initiators, the M_n control was poor because of an unfavorable mismatch between initiation and propagation rates. The molecular weight control with the "ate" complex 21 was better, but the ROP was slow. The best-behaved initiator in terms of living ROP was In(CH₂SiMe₃)₂(OⁱPr) (17). When used alone, In(CH₂SiMe₃)₃ was a very poor initiator, but in the presence of BnNH₂ amine-co-initiated immortal ROP occurred to give atactic amine-terminated PLA in a controlled manner. Use of InCl₃ and Et₃N in place of the indium alkyl gave a 4-fold increase in activity and a substantial increase in heterotacticity (P _r = 0.85). Initial studies showed that BnNH₂ and InCl ₃ alone could also produce heterotactically enriched, amine-terminated PLA at room temperature, albeit very slowly. (H ₂N₂^TsN^py = (2-NC₅H ₄)CH₂N(CH₂CH₂NHTs)₂; H₂N₂^TsN^OMe = MeOCH ₂CH₂N(CH₂CH₂NHTs)₂; H₂N₂^TsN^Ph = PhCH ₂N(CH₂CH₂NHTs)₂; H₂O ₂^MeN^py = (2-NC₅H₄)CH ₂N(CH₂ArOH)₂ (Ar = C₆H ₂Me₂).)

Full text of DOI:10.1021/om101166s

1202 Organometallics 2011, 30, 1202–1214
DOI: 10.1021/om101166s
Sulfonamide, Phenolate, and Directing Ligand-Free Indium Initiators for
the Ring-Opening Polymerization of rac-Lactide
Matthew P. Blake, Andrew D. Schwarz, and Philip Mountford*
Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K.
Received December 10, 2010
Reaction of In(CH2SiMe3)3 with H2N2TsNpy or H2N2TsNOMe gave the five-coordinate indium
alkyls In(N2TsNpy)(CH2SiMe3) (14) and In(N2TsNOMe)(CH2SiMe3) (15). The corresponding reac-
tion with H2N2TsNPh gave four-coordinate In(N2TsNPh)(CH2SiMe3) (16). Reaction of H2N2TsNpy
with In{N(SiMe3)2}3 gave the amide In(N2TsNpy){N(SiMe3)2} (19). Reaction of Na2N2TsNpy with
InCl3 in THF followed by LiOiPr gave the “ate” product In(N2TsNpy)(OiPr)Cl{Li(THF)} (21). The
chloride complex In(N2TsNpy)Cl(py) (22) was also isolated. Reaction of In(CH2SiMe3)3 with
H2O2MeNpy gave the bis(phenolate)amine compound In(O2MeNpy)(CH2SiMe3) (23), and reaction
i
with PrOH or Me2NCH2CH2OH gave the mixed alkyl-alkoxides In(CH2SiMe3)2(OiPr) (17) and
In(CH2SiMe3)2(OCH2CH2NMe2) (18), which are dimeric in the solid state. The X-ray structures of
14, 15, 17-19, and 21 - 23 have been determined. The compounds were evaluated as initiators for
the ring-opening polymerization of rac-lactide. With the alkyl and amide initiators, the Mn control
was poor because of an unfavorable mismatch between initiation and propagation rates. The
molecular weight control with the “ate” complex 21 was better, but the ROP was slow. The best-
behaved initiator in terms of living ROP was In(CH2SiMe3)2(OiPr) (17). When used alone,
In(CH2SiMe3)3 was a very poor initiator, but in the presence of BnNH2 amine-co-initiated immortal
ROP occurred to give atactic amine-terminated PLA in a controlled manner. Use of InCl3 and Et3N
in place of the indium alkyl gave a 4-fold increase in activity and a substantial increase in
heterotacticity (Pr = 0.85). Initial studies showed that BnNH2 and InCl3 alone could also produce
heterotactically enriched, amine-terminated PLA at room temperature, albeit very slowly. (H2N2TsNpy
=
(2-NC5H4)CH2N(CH2CH2NHTs)2; H2N2TsNOMe = MeOCH2CH2N(CH2CH2NHTs)2; H2N2TsNPh
= PhCH2N(CH2CH2NHTs)2; H2O2MeNpy = (2-NC5H4)CH2N(CH2ArOH)2 (Ar = C6H2Me2).)
Introduction
reviews,2k-r the supporting ligands “L” as well as the parti-
cular metal-initiating bond M-X have a profound influence
on both the rate and control of the ROP in terms of polymer
molecular weight, molecular weight distribution, and tacti-
city (in the case of lactide for example). These are key
parameters that help determine the macroscopic properties
of the polymers formed. In this contribution we report new
The controlled ring-opening polymerization (ROP) of
cyclic esters such as ε-caprolactone (ε-CL) or lactide (LA)
to form biocompatible or biodegradable thermoplastic ma-
terials has seen renewed and sustained interest from both a
molecular catalysis and materials chemistry point of view
over the last 10-15 years.1 Many approaches to the synthesis
of different polyesters via ROP are known,2 but in the work
described herein we focus on coordination complexes of the
type (L)M-X, which initiate and propagate the ROP of
cyclic monomers through a coordination-insertion mecha-
nism mediated through the M-X bond. As detailed in recent
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*To whom correspondence should be addressed. E-mail: philip.
mountford@chem.ox.ac.uk.
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pubs.acs.org/Organometallics
Published on Web 02/18/2011
2011 American Chemical Society

Article
Organometallics, Vol. 30, No. 5, 2011 1203
complexes and approaches to the ROP of rac-LA (the 1:1
mixture of L- and D-lactide) based on indium.
Within group 13, aluminum catalysts have been exten-
sively exploited for the ROP of rac-LA and other cyclic
esters, with many examples of predictable molecular weights,
narrow polydispersities (PDIs, i.e., Mw/Mn), and either
heterotactic or isotactic enrichment being achieved.2k-r By
way of example, notable aluminum-based catalysts are the
salen3 and salan4 complexes, with which highly isotactic,
syndiotactic, or tapered isotactic block copolymers can be
formed, depending on the stereoisomer of the LA and salen
ligands employed. Complexes of the related polydentate
phenoxy-amine ligands have also been investigated for the
ROP of both rac-LA and ε-caprolactone.5 In comparison to
the situation for aluminum, ROP initiators for the heavier
group 13 metals are very underdeveloped. One report for
gallium (S,S-[Me2Ga(μ-OCH(Me)CO2Me)]2) (for LA) ap-
peared very recently,6 and only a few reports for indium have
appeared (for ε-Cl and LA), mostly in the last two to three
years.7 The use of Al(OTf)3 and In(OTf)3 as heterogeneous
initiators for the ROP of L-LA at 100 °C in the melt with
added H2O co-initiator was reported by Kunioka et al.7a
The two triflate salts had similar activities, and PLA with
Mw/Mn = 1.12 was obtained for the indium system.
Figure 1. Previously reported ligand-supported indium com-
plexes for the ROP of LA.
rac-LA to isotactically enriched PLA in CH2Cl2 at RT within
30 min in a living manner. Okuda and co-workers’ bis-
(phenolate) indium isopropoxide In(O2S2)(OiPr) (3) also
initiated the ROP of L-LA but required higher temperatures
and longer reaction times.7d The ROP occurred in a
controlled manner as judged by narrow Mw/Mn values
(1.03-1.07), but there was no linear relationship between
Mn and monomer conversion, and with rac-LA only atactic
PLA was formed. The activity of 3 was lower than that of its
aluminum congener.5b A bis(phenolate)-supported indium
chloride was also recently reported by Wang and Sun et al.
High conversions to slightly heterotactically enriched PLA
in the presence of H2O or alcohol co-initiator were found
after 24 h at 110 °C.7h Arnold’s In(O,O0)2X compounds
The first report of a molecular indium ROP initiator was
by Huang et al. for the poly(pyrrolyl) systems 1 (Figure 1).7b
Broad PDIs and poor agreement between measured and
predicted Mn were reported for ε-CL. Mehrkhodavandi
and co-workers were the first to describe a highly active
and well-controlled molecular indium ROP initiator for
LA.7c The dimeric mixed mono(phenolate)-chloride system
In2(ONN0)2Cl2(μ-OEt)(μ-Cl) (2) converted 200 equiv of
t
(4, X = N(SiMe3)2, O-2,6-C6H3 Bu2, or O,O0; O,O0 = OCH-
(tBu)CH2P(O)tBu2) formed atactic or isotactically enriched
PLA.7g The polydispersities and extent of agreement be-
tween experimental and calculated Mn depended upon the
In-X group, solvent, time, and concentration. With the
homoleptic In(O,O0)3, 1248 equivs of rac-LA were converted
to PLA within 16 h at RT.
(3) (a) Spassky, N.; Wisniewski, M.; Pluta, C.; LeBorgne, A. Macro-
mol. Chem. Phys. 1996, 197, 2627. (b) Wisniewski, M.; Le Borgne, A.;
Spassky, N. Macromol. Chem. Phys. 1997, 198, 1227. (c) Ovitt, T. M.;
Coates, G. W. J. Polym. Sci. A: Polym. Chem. 2000, 38, 4686. (d) Ovitt,
T. M.; Coates, G. W. J. Am. Chem. Soc. 2002, 124, 1316. (e) Zhong, Z.;
Dijkstra, P. J.; Feijen, J. Angew. Chem., Int. Ed. 2002, 41, 4510. (f)
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Quisenberry, K. T.; Zhou, Z. Inorg. Chem. 2008, 47, 2613.
One of the more remarkable advances in indium-initiated
ROP has been Hillmyer and Tolman et al.’s report of the fast
and highly controlled formation of heterotactic PLA from rac-
LA using an InCl3:BnOH:Et3N directing ligand-free system.7e,f
Narrow polydispersities (e1.10) and Pr (probability of racemic
enchainment) values of up to 0.97 were reported, along with
a detailed study of the coordinative-insertion mechanism, and
model complexes for the postulated active catalyst in these
systems.
Given the emerging interest in indium initiators for the
ROP of cyclic esters, we have extended our own efforts into
this area. We recently described five- and four-coordinate
bis(sulfonamide)amine complexes of the type Al(N2TsNL)-
(OR) (5-7, Figure 2) as new aluminum initiators for the
ROP of rac-LA,8c along with a series of group 4 complexes
such as 8 and 9.8a,b In these group 4 and 13 catalysts, the
electron-withdrawing SO2R substituents reduce the usual basi-
city of anionic amide donors “NR2” and therefore allow them
to act in some regard as “phenolate mimics”. Compounds
of the type 5-9 are initiators for the ROP of rac-LA, giving
(4) Hormnirun, P.; Marshall, E. L.; Gibson, V. C.; White, A. J. P.;
Williams, D. J. J. Am. Chem. Soc. 2004, 126, 2688.
(5) (a) Alcazar-Roman, L. M.; O’Keefe, B. J.; Hillmyer, M. A.;
Tolman, W. B. Dalton Trans. 2003, 3082. (b) Ma, H.; Melillo, G.; Oliva,
L.; Spaniol, T. P.; Englert, U.; Okuda, J. Dalton Trans. 2005, 721. (c)
Tang, Z.; Gibson, V. C. Eur. Polym. J. 2007, 43, 150. (d) Johnson, A. L.;
Davidson, M. G.; Perez, Y.; Jones, M. D.; Merle, N.; Raithby, P. R.;
Richards, S. P. Dalton Trans. 2009, 5551.
ꢀ
(6) Horeglad, P.; Kruk, P.; Pecaut, J. Organometallics 2010, 29, 3729.
(7) (a) Kunioka, M.; Wang, Y.; Onozawa, S.-Y. Macromol. Symp.
2005, 224, 167. (b) 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. (c) Douglas, A. F.; Patrick, B. O.; Mehrkhodavandi, P.
Angew. Chem. Int. Ed. 2008, 47, 2290. (d) Peckermann, I.; Kapelski, A.;
Spaniol, T. P.; Okuda, J. Inorg. Chem. 2009, 48, 5526. (e) Pietrangelo, A.;
Hillmyer, M. A.; Tolman, W. B. Chem. Commun. 2009, 2736. (f)
Pietrangelo, A.; Knight, S. C.; Gupta, A. K.; Yao, L. J.; Hillmyer,
M. A.; Tolman, W. B. J. Am. Chem. Soc. 2010, 132, 11649. (g)
Buffet, J.-C.; Okuda, J.; Arnold, P. L. Inorg. Chem. 2010, 49, 419. (h)
Hu, M.; Wang, M.; Zhang, P.; Wang, L.; Zhu, F.; Sun, L. Inorg. Chem.
Commun. 2010, 13, 968.

1204 Organometallics, Vol. 30, No. 5, 2011
Blake et al.
Figure 3. Protio forms of the ligands used in this study.8c,9-11
(10),9 H2N2TsNOMe (11),10 and H2N2TsNPh (12),8c along with
the related bis(phenol)amine H2O2MeNpy (13)11 (Figure 3), were
synthesized according to the literature methods. Initial complexa-
tion studies (Scheme 1) focused on alkyl complexes, which we
hoped would act as intermediates en route to the more desirable
alkoxide initiators via protonolysis reactions with alcohols,
according to certain literature precedent.12 We used In(CH2-
SiMe3)3 as our primary starting alkyl reagent because of its con-
venient solubility and ease of preparation,13 storage, and handling.
Reaction of H2N2TsNpy or H2N2TsNOMe with In(CH2SiMe3)3
in toluene at 70 °C for 16 h gave the five-coordinate complexes
In(N2TsNpy)(CH2SiMe3) (14) and In(N2TsNOMe)(CH2SiMe3)
(15) inca. 60-70% isolated yield, respectively (Scheme 1). When
Figure 2. Examples of aluminum and group 4 ROP initiators
supported by poly(sulfonamide)amine ligands.8
Scheme 1. Synthesis of the New Indium Alkyl Complexes
In(N2TsNL)(CH2SiMe3) (14-16)
1
followed by H NMR spectroscopy in C6D6 the conversions
were quantitative and the expected SiMe4 side-product was
observed. Similarly, reaction of H2N2TsNPh withIn(CH2SiMe3)3
gave four-coordinate In(N2TsNPh)(CH2SiMe3) (16) in 81%
yield. The protonolysis routes in Scheme 1 are analogous to
those used previously by us for the aluminum congeners Al-
(N2TsNL)Et (L = py, OMe, or Ph)8c and more generally by
Okuda and Atwood et al. for bis(phenolate) or Schiff base O2S2-
and O2N2-donor ligands, for example.7d,14
The solution NMR data are consistent with the pro-
posed structures, indicating Cs molecular symmetry. For
example, the diastereotopic methylene hydrogens of the
NCH2CH2NTs arms appear as a series of four multiplets,
whereas those for the NCH2R (R = 2-NC5H4 or Ph) linkage
in 14 and 16 are singlets. The 1H NMR shift (δ = 8.74 ppm)
of the 2-position hydrogen atom of the pyridyl donor in 14 is
significantly shifted from that in the free protio ligand (δ =
8.58 ppm in the same solvent), consistent with coordination
to indium. The X-ray structures of compounds 14 and 15
have been determined and are compared in Figure 4. Selected
distances and angles are listed in Tables 1 and 2. Diffraction-
quality crystals of 16 could not be grown, but its structure is
expected to be comparable to that of the aluminum congener
Al(N2TsNPh)Et.8c
well-defined molecular weights and molecular weight distribu-
tions in solution as well as in the melt at 130 °C. Here we report
our recent results with indium bis(sulfonamide)amine com-
plexes, along with related work using a bis(phenolate)amine
initiator. We also describe initial studies of the amine co-
initiated ROP of rac-LA using InCl3 or In(CH2SiMe3)3.
The solid-state structures of 14 and 15 confirm the five-
coordinate structures expected on the basis of the NMR
(10) Bailey, N. A.; Fenton, D. E.; Hellier, P. C.; Hempstead, P. D.;
Casellatob, U.; Vigatob, P. A. J. Chem. Soc., Dalton Trans. 1992, 2809.
(11) Toupance, T.; Dubberley, S. R.; Rees, N. H.; Tyrrell, B. R.;
Mountford, P. Organometallics 2002, 21, 1367.
Results and Discussion
(12) (a) Peng, K.-F.; Chen, C.-T. Dalton Trans. 2009, 9800. (b) Ma,
H. Y.; Okuda, J. Macromolecules 2005, 38, 2665.
Synthesis and Structural Studies. The tridentate and tetra-
dentate bis(sulfonamide)amine protio-ligands H2N2TsNpy
(13) (a) Peckermann, I.; Robert, D.; Englert, U.; Spaniol, T. P.;
Okuda, J. Organometallics 2008, 27, 4817. (b) Kopasz, J. P.; Hallock,
R. B.; Beachley, O. T. Inorg. Synth. 1986, 24, 89. (c) Beachley, O. T.;
MacRae, D. J.; Churchill, M. R.; Kovalevsky, A. Y.; Robirds, E. S.
Organometallics 2003, 22, 3991.
(14) (a) Hill, M. S.; Atwood, D. A. Main Group Chem. 1998, 2, 191.
(b) Atwood, D. A.; Jegier, J. J.; Rutherford, D. Bull. Chem. Soc. Jpn.
1997, 70, 2093. (c) Peckermann, I.; Dols, T. S.; Spaniol, T. P.; Okuda, J.
J. Organomet. Chem. 2010, 695, 2325.
(8) (a) Schwarz, A. D.; Thompson, A. L.; Mountford, P. Inorg. Chem.
2009, 48, 10442. (b) Schwarz, A. D.; Herbert, K. R.; Paniagua, C.;
Mountford, P. Organometallics 2010, 29, 4171. (c) Schwarz, A. D.; Chu,
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(9) Skinner, M. E. G.; Li, Y.; Mountford, P. Inorg. Chem. 2002, 41,
1110.

Article
Organometallics, Vol. 30, No. 5, 2011 1205
˚
Table 2. Selected Bond Distances (A) and Angles (deg) for
In(N2TsNOMe)(CH2SiMe3) (15)
In(1)-N(1)
2.122(3)
2.170(2)
2.348(2)
96.46(10)
95.68(10)
129.52(11)
In(1)-O(5)
In(1)-C(22)
2.567(2)
2.127(3)
In(1)-N(2)
In(1)-N(3)
N(1)-In(1)-N(2)
N(1)-In(1)-O(5)
N(1)-In(1)-C(22)
N(2)-In(1)-O(5)
N(3)-In(1)-C(22)
139.67(8)
143.86(11)
trigonal-bipyramidal geometries depicted in Scheme 1. This
is best illustrated by the different NTs-In-L (L = py or OMe
donor) angles in the two compounds (85.52(13)° and
140.87(11)° in 14 and 95.68(10)° and 139.67(8)° in 15).
A similar distortion was seen in the aluminum congener
Al(N2TsNpy)Et (corresponding values 101.95(7)° and
133.77(8)°). The SiMe3 group in 14 and 15 is oriented into
the wider NTs-In-L aperture. The solution NMR data
indicate that the structural variations are averaged on the
NMR time scale.
As mentioned, it was hoped that the new indium alkyls
would serve as entry points to the corresponding alkoxide
complexes, which are usually superior initiators for ROP.
Unfortunately, there was no reaction between 14-16 and
iPrOH in benzene either at room temperature or on heating.
Attempted synthesis of In(N2TsNpy)(OR) (R = Pr or Bu)
from H2N2TsNpy (10) and In(OR)3 under a range of condi-
tions led only to mixtures of unknown products, presumably
due to the lower Brønsted acidity of 10 compared to the
ROH, which was intended to be displaced.
i
t
Figure 4. Displacement ellipsoid plots of In(N2TsNpy)(CH2SiMe3)
(14, top) and In(N2TsNOMe)(CH2SiMe3) (15, bottom). H atoms are
omitted for clarity. Ellipsoids are drawn at the 20% probability level.
We have previously shown that Al(N2TsNL)(OiPr) (L = py
(5) or Ph (6)) and Al(N2TsNpy)(OCH2CH2NMe2) (7)
(Figure 2) are readily obtained from AlEt2(OR) and the
respective protio-ligands.8c Likewise, salen-supported in-
dium halide compounds have been prepared from the corre-
sponding protio-ligands and InEt2X (X = Cl, Br).14a The
mixed dialkyl-alkoxide complexes In(CH2SiMe3)2(OiPr)
(17) or In(CH2SiMe3)2(OCH2CH2NMe2) (18) were prepared
in ca. 95% yield from the corresponding alcohol and In-
(CH2SiMe3)3 (eq 1). They have been structurally character-
ized as dimers in the solid state, and further details are given
in the Supporting Information. Disappointingly, reaction of
H2N2TsNL with 17 gave only the corresponding alkyl com-
pounds 14-16. Following the reactions on the NMR tube
scale in C6D6 confirmed the formation of the respective
alcohols and SiMe4. Analogous results were found with 18,
which we had hoped would have a less readily displaced
alkoxide ligand due to the chelating NMe2 group.
˚
Table 1. Selected Bond Distances (A) and Angles (deg) for
In(N2TsNpy)(CH2SiMe3) (14)
In(1)-N(1)
2.132(4)
2.205(3)
2.380(3)
In(1)-N(4)
In(1)-C(25)
2.429(3)
2.138(4)
In(1)-N(2)
In(1)-N(3)
N(1)-In(1)-N(2)
N(1)-In(1)-N(4)
N(1)-In(1)-C(25)
104.82(14)
85.52(13)
128.47(15)
N(2)-In(1)-N(4)
N(3)-In(1)-C(25)
140.87(11)
147.94(15)
˚
data. The In-CH2 bond lengths (av 2.133(3) A) are within
the known range for In-CH2SiMe3 ligands (2.106-2.251
(av 2.17(4)) A, 27 examples),15 but shorter than in the homo-
˚
13a
˚
leptic starting compound In(CH2SiMe3)3 (av 2.178(4) A).
˚
The In-NTs distance (av 2.157, range 2.122(3)-2.205(3) A)
is somewhat longer than terminal indium amide bonds
˚
(L)In-NR2 in general (2.021-2.170 (av 2.10(4) A),
9 examples)15 and also, for example, the In-Npyrrolyl dis-
tances in 1 (Figure 1, av 2.122(1) A). This is attributed to the
˚
electron-withdrawing nature of the -SO2Tol substituents as
discussed previously.8 Only one other indium sulfonamide
compound has been structurally characterized, namely, the
dimeric [In(CH2SiMe3)2(μ-κN,O-N{SO2Me)2}]2, in which
16
˚
the average In-N distance was 2.338(3) A. The In-CH2
and In-NTs distances are on average slightly longer in 14
compared to 15, apparently because of the better donor
nature of the pyridyl moiety in N2TsNpy compared to -OMe
in N2TsNOMe
.
Closer examination of the structures of 14 and 15 show they
are somewhat distorted from the idealized Cs symmetric,
Seeking an alternative approach to the target In(N2TsNL)-
(OR) compounds, we prepared the amide complex In(N2TsNpy)-
{N(SiMe3)2} (19) from H2N2TsNpy and In{N(SiMe3)2}3 in 68%
yield (eq 2). The NMR data for 19 are comparable to those for 14
(15) Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J. Chem. Inf.
Comput. Sci. 1996, 36, 746 (The UK Chemical Database Service: CSD
version 5.31 updated August 2010).
(16) Blaschette, A.; Michalides, A.; Jones, P. G. J. Organomet. Chem.
1991, 411, 57.

1206 Organometallics, Vol. 30, No. 5, 2011
Blake et al.
In(N2TsNpy)Cl(py) (22) as a sparingly soluble, six-coordinate
monomer. The molecular structure is shown in Figure 6, and
selected distances and angles are presented in Table 4.
Reaction of the in situ generated 20 with LiOiPr gave a
soluble product identified by single-crystal X-ray diffraction
as the “ate” complex In(N2TsNpy)(OiPr)Cl{Li(THF)} (21).
The molecular structure of 21 is shown in Figure 7, and
selected distances and angles are given in Table 5. Attempts
to liberate the bound LiCl from 21 (e.g., by heating in toluene)
were unsuccessful, as were efforts to prepare a nonate product
by reaction of 20 with NaOiPr, which gave mixtures of
products. No reaction occurred when Na2N2TsNpy and In-
(OTf)3 were heated in pyridine-d5 at 70 °C for several days.
The solid-state structure of 21 (Figure 7) shows the pre-
sence of a formally anionic, six-coordinate indium center
bound to a tetradentate N2TsNpy donor as well as to a
chloride and an isopropoxide ligand. The charge is balanced
by an approximately tetrahedrally coordinated Li, which is
bound to the isopropoxide oxygen, two sulfonyl oxygens,
and a residual THF. The coordination environment leads to
C1 molecular symmetry, and the solution NMR data
(CD2Cl2) are consistent with this (inequivalent OCHMe2
methyl groups and four 13C methylene shifts for the
chemically inequivalent CH2CH2NTs arms of N2TsNpy).
The In-NTs distances are rather different (In(1)-N(1) =
Figure 5. Displacement ellipsoid plot of In(N2TsNpy){N-
(SiMe3)2} (19). H atoms are omitted for clarity. Ellipsoids are
drawn at the 20% probability level.
˚
Table 3. Selected Bond Distances (A) and Angles (deg) for
In(N2TsNpy){N(SiMe3)2} (19)
In(1)-N(1)
2.176(3)
2.116(3)
2.459(3)
In(1)-N(4)
In(1)-N(5)
2.326(3)
2.084(3)
˚
In(1)-N(2)
2.189(5), In(1)-N(2) = 2.258(6) A) since one nitrogen is
In(1)-N(3)
trans to the In-Cl group and the other trans to pyridyl. The
structure of 21 can be compared with that of the Cs sym-
metric In(N2TsNpy)Cl(py) (22), which also possesses a six-
N(1)-In(1)-N(4)
N(1)-In(1)-N(2)
N(2)-In(1)-N(3)
130.62(12)
104.82(14)
77.24(11)
N(2)-In(1)-N(4)
N(2)-In(1)-N(5)
N(3)-In(1)-N(5)
96.28(12)
132.44(13)
147.91(12)
˚
coordinate indium center. The average In-NTs (2.224(4) A)
˚
except that the resonances for CH2SiMe3 group in the latter are
replaced by the singlet of the N(SiMe3)2 group.
and In-Cl (2.4942(18) A) bond distances in 21 are longer
than those in 22 (2.209(3) and 2.4022(11) A, respectively).
˚
This is partly due to the formally anionic nature of the
indium center in 21 and to the In-Cl bond in 21 being
positioned trans to In-NTs, whereas in 22 it lies trans to
N(3), which is a weaker donor.
As mentioned, there have already been reports of the use
of phenolate ligand-supported indium complexes as ROP
initiators.7c,d,h Mehrkhodavandi and co-workers’ compound 2
contains a tridentate mono(phenolate), whereas Okuda and
co-workers’ compound 3 and its homologues have a bis-
(phenolate) ligand with an O2S2 donor set. To extend the
range of this type of compound (which have been very
successful for aluminum5 and the group 3 and lanthanide
metals2p,q,17), and to make further comparisons with the
N2TsNpy-supported systems, we also attempted to prepare a
series of indium complexes starting from H2O2MeNpy (13,
Figure 3).
Diffraction-quality crystals of 19 were grown from a
cold toluene solution. The molecular structure is shown in
Figure 5, and selected distances and angles are presented in
Table 3. Like 14 and 15, the geometry of 19 is distorted from
trigonal bipyramidal toward square-based pyramidal (for
example, NTs-In-Npy = 96.28(12)° and 130.62(12)°). The
˚
In-N(SiMe3)2 distance of 2.176(3) A is longer than any
˚
reported previously (2.021-2.170 (av 2.10(4) A) for 9
examples),15 although most of the previous examples contain
only three- or four-coordinate metals. The shorter In-N
˚
distance of 2.101(2) A in Arnold et al.’s five-coordinate In(O,
O0)2{N(SiMe3)2} (4, X = N(SiMe3)2) is attributed to the
poorer donor ability of the O,O0 ligands in this system.
Unfortunately, despite the longer In-N(SiMe3)2 bond in
19 and the successful conversion of In(O,O0)2{N(SiMe3)2}
to In(O,O0)2(OAr) on treatment with ArOH (Ar = 2,6-
t
i
C6H3 Bu2),7g reaction of 19 with PrOH gave an unknown
mixture of products.
Reaction of H2O2MeNpy with In(CH2SiMe3)3 proceeded
smoothly at RT to give In(O2MeNpy)(CH2SiMe3) (23) in
good yield (eq 3). Attempted replacement of the alkyl group
Salt-elimination/metathesis routes to bis(sulfonamide)-
supported indium alkoxides were also explored as shown in
Scheme 2. Reaction of Na2N2TsNpy with InCl3 in THF gave a
very insoluble material formulated as “In(N2TsNpy)Cl” (20),
which is probably oligomeric in the solid state. Direct
support for the presence of 20 was obtained by Soxhlet
extraction into refluxing pyridine over 48 h, which gave
(17) Dyer, H. D.; Huijser, S.; Susperregui, N.; Bonnet, F.; Schwarz,
A. D.; Duchateau, R.; Maron, L.; Mountford, P. Organometallics 2010,
29, 3602.

Article
Organometallics, Vol. 30, No. 5, 2011 1207
Scheme 2. Synthesis of In(N2TsNpy)(OiPr)Cl{Li(THF)} (21) and In(N2TsNpy)Cl(py) (22)
˚
Table 4. Selected Bond Distances (A) and angles (deg) for
In(N2TsNpy)Cl(py) (22)
In(1)-N(1)
2.204(4)
2.213(4)
2.344(3)
147.05(13)
86.49(14)
90.95(14)
In(1)-N(4)
2.314(3)
2.336(4)
2.4022(11)
85.32(14)
169.11(9)
171.22(12)
In(1)-N(2)
In(1)-N(5)
In(1)-N(3)
In(1)-Cl(1)
N(1)-In(1)-N(2)
N(1)-In(1)-N(4)
N(1)-In(1)-N(5)
N(2)-In(1)-N(5)
N(3)-In(1)-Cl(1)
N(4)-In(1)-N(5)
to Okuda and co-workers’ O2S2-type systems.7d,14c The In-CH2
distance of 2.159(3) A in 23 is slightly longer than those in
˚
In(N2TsNL)(CH2SiMe3) (L = py (14) or OMe (15); 2.138(4)
˚
and 2.127(3) A, respectively). Okuda and co-workers’ com-
plexes of O2S2-donor bis(phenolate) ligands have In-CH2SiMe3
distances of 2.127(2) and 2.144(13) A. As mentioned, the average
In-CH2 distance in In(CH2SiMe3)3 was 2.178(4) A.
Figure 6. Displacement ellipsoid plot of In(N2TsNpy)Cl(py)
(22). H atoms are omitted for clarity. Ellipsoids are drawn at
the 20% probability level.
˚
13a
˚
ROP of rac-LA in Solution. Table 7 summarizes the ROP
results for the complexes 14-16, 19, 21, and 23. Results for
In(CH2SiMe3)3 and In(CH2SiMe3)2(OiPr) (17) are also given
for comparison and are discussed below. Experiments were
performed in toluene at 70 °C with a [rac-LA]0:[In] ratio
of 100:1 ([rac-LA]0 represents the initial monomer con-
centration), and under these conditions all the complexes
were found to be active. The progress of each run was
monitored by aliquot sampling, and the molecular weights
and PDIs (Mw/Mn) were determined by GPC using the
appropriate Mark-Houwink corrections for PLA.19 Plots
of % conversion vs time, Mn and PDI vs % conversion, and
kinetic analyses are provided in the SI (Figures S2-S7).
Figure 9 shows these data for In(N2TsNpy){N(SiMe3)2} (19)
as a representative example of the indium-alkyl and -amide
systems. Experiments were also attempted in CH2Cl2 solu-
tion at RT with the same [rac-LA]0 and [rac-LA]0:[In]
ratio. The ROP in these cases was considerably slower.
For example, there was a ca. 50-fold difference in kapp
i
in 23 by reaction with PrOH gave mixtures of products,
reminiscent of Okuda and co-workers’ report of similarly dis-
appointing outcomes for In(O2S2)(CH2SiMe3) in an attempt
to prepare 3 by protonolysis.7d Unfortunately, reaction of H2-
O2MeNpy with In{N(SiMe3)2}3 or In(OR)3 also gave unknown
mixtures, while reaction with In(CH2SiMe3)2(OiPr) formed 23.
Diffraction-quality crystals of 23 were grown from a
saturated toluene solution layered with pentane. The molec-
ular structure is shown in Figure 8, and selected distances
and angles are given in Table 6. The coordination geometry
at indium in 23 is best described as square-based pyramidal
with O(1) occupying the apical position. This podand type of
bis(phenolate)amine ligand has a strong tendency to occupy
four vertices of an octahedron,11,18 and aluminum complexes
of homologous ligands have been shown to have analogous
solid-state structures to that of 23.5a The In-O and In-N
distances are within the usual ranges.15 Several related Schiff
base analogues of 23 have been reported14a,b in addition
(19) (a) Rudin, A.; Hoegy, H. L. W. J. Polym. Sci., Part A: Polym.
ꢀ ^
ꢀ
(18) (a) Chmura, A. J.; Davidson, M. G.; Jones, M. D.; Lunn, M. D.;
Mahon, M. F.; Johnson, A. F.; Khunkamchoo, P.; Roberts, S. L.;
Wong, S. S. F. Macromolecules 2006, 39, 7250. (b) Tshuva, E.; Goldberg,
I.; Kol, M.; Weitman, H.; Goldschmidt, Z. Chem. Commun. 2000, 379.
Chem. 1972, 10, 217. (b) Barakat, I.; Dubois, P.; Jerome, R.; Teyssie, P.
J. Polym. Sci., Part A: Polym. Chem. 1993, 31, 505. (c) Dorgan, J. R.;
Janzen, J.; Knauss, D. M.; Hait, S. B.; Limoges, B. R.; Hutchinson,
M. H. J. Polym. Sci., Part B: Polym. Phys. 2005, 43, 3100.

1208 Organometallics, Vol. 30, No. 5, 2011
Blake et al.
Figure 7. Displacement ellipsoid plot of In(N2TsNpy)(OiPr)Cl{Li(THF)} (21). H atoms are omitted for clarity. Ellipsoids are drawn at
the 20% probability level.
˚
˚
Table 5. Selected Bond Distances (A) and Angles (deg) for
Table 6. Selected Bond Distances (A) and Angles (deg) for
In(N2TsNpy)(OiPr)Cl{Li(THF)} (21)
In(O2MeNpy)(CH2SiMe3) (23)
In(1)-N(1)
2.189(5)
2.258(6)
2.326(5)
2.306(5)
2.057(4)
2.4942(18)
1.436(5)
92.0(2)
S(1)-O(2)
1.456(5)
1.438(5)
1.443(6)
1.958(13)
1.958(15)
1.899(15)
1.890(13)
168.54(18)
114.9(8)
104.0(6)
112.0(7)
In(1)-N(1)
2.341(2)
2.350(3)
2.091(2)
88.95(8)
90.18(8)
153.59(8)
In(1)-O(2)
In(1)-C(25)
2.115(2)
2.159(3)
In(1)-N(2)
S(2)-O(3)
In(1)-N(2)
In(1)-N(3)
S(2)-O(4)
In(1)-O(1)
In(1)-N(4)
Li(1)-O(2)
O(1)-In(1)-O(1)
O(1)-In(1)-N(2)
O(2)-In(1)-N(2)
O(2)-In(1)-O(2)
N(1)-In(1)-C(25)
103.18(8)
149.03(11)
In(1)-O(5)
Li(1)-O(3)
In(1)-Cl(1)
Li(1)-O(5)
S(1)-O(1)
Li(1)-O(6)
detected in the MALDI-ToF mass spectra. The silylamide 19
also produced PLA with Mn higher than calculated for one
chain per metal center, either in toluene at 70 °C (entry 5 and
Figure 9) or CH2Cl2 at RT (SI, Figure S5). The Mn
and Mw/Mn vs % conversion plots (Figure 9 and SI Figures
S2-S5) for all of these systems are similar. Thus the Mn
increases almost immediately and rapidly in the very early
stages of the ROP, then more steadily thereafter in a linear
fashion with respect to % conversion. The slopes of the Mn vs
% conversion plots in this latter region were in the range
308(14)-1214(90) g mol-1 (% conversion)-1, larger than
the ideal value for [rac-LA]0:[In] = 100:1 (144.1 g mol-1
(% conversion)-1). These values suggest that, at most, only
between ca. 15% and 50% of the total indium present enters
the catalytic cycle. Such characteristics are consistent with
previous literature reports for metal-alkyl and -amide
initiators and are interpreted in terms of the recognized
mismatch between the rates of initiation (insertion into
M-alkyl or M-amide) and propagation (insertion into
M-O of the growing polymeryl chain).12b,17,20 Interestingly,
Mw/Mn remained constant or increased only slightly within
the fairly narrow range ca. 1.06-1.17 throughout the ROP,
suggesting that once polymerization is underway, there is
relatively little transesterification or other side reactions.
After an induction period in some instances, rac-LA con-
sumption for the alkyl and amide initiators followed well-
behaved first-order kinetics. Apparent first-order propagation
rate constants, kapp, were measured from the corresponding
semilogarithmic plots of ln([LA]0/[LA]t) vs time. The kapp values
N(1)-In(1)-N(2)
N(1)-In(1)-Cl(1)
N(2)-In(1)-N(4)
N(4)-In(1)-Cl(1)
N(3)-In(1)-O(5)
O(2)-Li(1)-O(3)
O(2)-Li(1)-O(5)
O(2)-Li(1)-O(6)
90.20(14)
84.45(19)
86.25(14)
Figure 8. Displacement ellipsoid plot of In(O2MeNpy)(CH2SiMe3)
(23). H atoms are omitted for clarity. Ellipsoids are drawn at the
20% probability level.
(apparent first-order rate constant) between the two sets of
conditions for 19 (one of the fastest sulfonamide-supported
initiators studied, cf. Figure 9 and S5 of the SI). Similar
differences were found for In(CH2SiMe3)2(OiPr) (17; cf.
entry 8, Table 7, and entry 5, Table 9).
Entries 1-4 are for the four alkyl compounds 14-16
and 23. All give PLA with much higher than predicted Mn
values. The expected -C(O)CH2SiMe3 end groups could be
(20) (a) Chamberlain, B. M.; Cheng, M.; Moore, D. R.; Ovitt, T. M.;
Lobkovsky, E.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 3229. (b)
Chisholm, M. H.; Gallucci, J. C.; Phomphrai, K. Inorg. Chem. 2002, 41,
2785. (c) Chisholm, M. H.; Gallucci, J. C.; Phomphrai, K. Inorg. Chem.
2005, 44, 8004.

Article
Organometallics, Vol. 30, No. 5, 2011 1209
Table 7. ROP of rac-LA in Solution with Various Indium Compoundsa
c
entry
initiator
conversion (%)b
time (h)
kapp
Mn (GPC)d
Mn (calcd)e
Mw/Mn
1
2
3
4
5
6
7
8
In(N2TsNpy)(CH2SiMe3) (14)
In(N2TsNOMe)(CH2SiMe3) (15)
In(N2TsNPh)(CH2SiMe3) (16)
In(O2MeNpy)(CH2SiMe3) (23)
In(N2TsNpy){N(SiMe3)2} (19)
In(N2TsNpy)(OiPr)Cl{Li(THF)} (21)
In(CH2SiMe3)3
88
72
89
94
81
83
74f
92
5
95
94
6
0.52(2)
0.013(1)
0.027(2)
0.76(1)
0.64(4)
58 680
88 280
88 050
41 640
34 200
11 910
78 880
13 260
12 772
10 466
12 916
13 636
11 836
12 020
10 754
13 320
1.06
1.15
1.16
1.07
1.14
1.54
1.09
1.17
3
98
12
9
0.049(1)
g
In(CH2SiMe3)2(OiPr) (17)
0.29(1)
a Conditions: [rac-LA]0:[In] = 100:1, 4.0 mL of toluene at 70 °C, [rac-LA]0 = 1.00 M. See Experimental Section for other details. All PLAs formed
were atactic. b NMR conversion. c Apparent rate constant with units h-1 or M-1 h-1 derived from the first- or second-order log plots, respectively (all
systems were first-order with respect to rac-LA except for entry 6; see the SI for further details). d Molecular weights (g mol-1) determined by GPC in
THF at 30 °C using the appropriate Mark-Houwink corrections. e Expected Mn (g mol-1) for 1 linear chain per metal center at the stated % conversions
assuming CH2SiMe3 (entries 1-4 and 7), N(SiMe3)2 (entry 5), or isopropoxide (entries 6 and 8, verified by MALDI-ToF-MS) initiating groups. f Low
conversion due to gel formation. g kapp not measured.
0.013(2) and 0.027(2) h-1 for 15 and 16), pointing to a consider-
able beneficial effect of a pyridyl pendant donor in N2TsNpy
compared to the weaker -OMe moiety in N2TsNOMe or none in
N2TsNPh, respectively. The indium-silylamide 19 (with the same
pyridyl-donor supporting ligand) had kapp = 0.64(6) h-1
,
identical to that of 14 within error. This is consistent with the
same type and concentration of propagating species being
formed once initiation had occurred. The bis(phenolate)amine
compound 23 had kapp = 0.76(1) h-1, comparable to that of 14
and 19.
As mentioned, the three fastest initiators 14, 19, and 23
had the smallest gradients in their Mn vs % conversion plots,
by a factor of ca. 3 (i.e., 316(20), 364(12), and 308(14),
respectively, vs 1163(90) and 1082(28) g mol-1 (% con-
version)-1 for 15 and 16). However, even if these reflect the
amounts of active catalyst in the systems, the combined
results still suggest that the intrinsic kprop value for the active
species formed with N2TsNpy is an order of magnitude larger
than those for N2TsNOMe and N2TsNPh. Interestingly, in
previous studies of the ROP of rac-LA by M(N2TsNL)(OiPr)2
(M = Ti or Zr; L = py or OMe) we found that kapp for the
compounds with L = py were lower than for L = OMe by up
to an order of magnitude.8a On the other hand, the three
aluminum systems Al(N2TsNL)OR (L = py, OMe, or Ph;
R = CH2CH2NH2) gave almost identical activities and
molecular weight control, regardless of the L group.8c Overall
there does not seem to be a consistent effect of the various L
groups on kapp or performance between different metals and
catalyst systems. We have shown previously that kapp for ROP
by Zr(O2MeNpy)(OiPr)2 was ca. twice that for Zr(N2TsNpy)-
(OiPr)2, consistent with the relative kapp values for 14 and 23.8a
The “ate” complex In(N2TsNpy)(OiPr)Cl{Li(THF)} (21,
entry 6) also gave slow ROP with only 83% conversion after
98 h. However, the agreement between measured and ex-
pected molecular weight was considerably better than for the
alkyl or silylamide systems, as shown by the linear Mn vs %
conversion plot (SI, Figure S6) with a gradient of 143(9) g
mol-1 (% conversion)-1, identical within error to that ex-
pected (144.1 g mol-1 (% conversion)-1) for one polymer
chain growing per indium center. This reflects the above-
mentioned superior initiating ability of alkoxides compared
Figure 9. Data for the ROP of rac-LA using In(N2TsNpy){N-
(SiMe3)2} (19). (Top) % conversion vs time. (Middle) Mn
(diamonds) and Mw/Mn (circles) vs % conversion; the gradient
of the Mn vs conversion plot is 364(12) g mol-1 (% con-
version)-1 (R2 = 0.994). (Bottom) First-order plot for rac-LA
consumption; R2 = 0.990, kapp = 0.64(4) h-1. Conditions: [rac-
LA]0:[In] = 100:1, 4.0 mL of toluene at 70 °C, [rac-LA]0 =
1.00 M.
1
to alkyls and amides. The H NMR and MALDI-ToF MS
data were consistent with iPrO-terminated PLA. Disappoint-
ingly, there was a steady increase in Mw/Mn from 1.07 to 1.54
during the course of the polymerization, indicative of some
instability in this system. Interestingly, kinetic analysis
showed that the rac-LA was consumed in a second-order
fashion, which might reflect a role of the lithium center as well
are dependent on both the actual propagation rate constant
(kprop) and the effective concentration of active indium catalyst.
Of the sulfonamide-supported alkyl compounds, 14 had the
largest kapp by about a factor of around 25 on average (0.52(2) vs

1210 Organometallics, Vol. 30, No. 5, 2011
Table 8. ROP of rac-LA in the Melt with Various Indium Compoundsa
Blake et al.
entry
initiator
conversion (%)b
Mn (GPC)c
Mn (calcd)d
Mw/Mn
1
2
3
4
5
6
7
8
In(N2TsNpy)(CH2SiMe3) (14)
In(N2TsNOMe)(CH2SiMe3) (15)
In(N2TsNPh)(CH2SiMe3) (16)
In(O2MeNpy)(CH2SiMe3) (23)
In(N2TsNpy){N(SiMe3)2} (19)
In(N2TsNpy)(OiPr)Cl{Li(THF)} (21)
In(CH2SiMe3)3
88
71
66
98
70
72
95
97
70 580
39 870
64 950
139 010
23 250
15 740
94 440
38 180
38 138
30 788
28 626
42 462
30 429
31 192
41 165
42 002
1.68
3.22
2.57
1.39
1.36
1.22
1.56
1.66
In(CH2SiMe3)2(OiPr) (17)
a Conditions: [rac-LA]0:[In] = 300:1 at 130 °C for 2 h. See Experimental Sections for other details. All PLAs formed were atactic. b NMR conversion.
c Molecular weights (g mol-1) determined by GPC in THF at 30 °C using the appropriate Mark-Houwink corrections. d Expected Mn (g mol-1) for 1
linear chain per metal center assuming CH2SiMe3 (entries 1-5), N(SiMe3)2 (entry 6), or isopropoxide (entries 7 and 8).
as theindium one. Theslow ROP with 21 maybe attributed to
the six-coordinate indium and possible coordination of
lithium to the active catalyst, as in 21 itself. Polymerizations
with 21 were also performed in THFandinthepresence of 12-
crown-4 in an attempt to sequester the lithium. Unfortu-
nately, there was no improvement in rate or other perfor-
mance figures. As with the alkyl and amide initiators, the
PLA formed with 21 was atactic (Pr ≈ 0.5, i.e., within error).
Entries 7 and 8 of Table 7 are for In(CH2SiMe3)3 and
In(CH2SiMe3)2(OiPr) (17) to allow a further comparison of
indium-alkyl and indium-alkoxide initiating groups. The
tris(alkyl) compound formed high molecular weight PLA
(78880 g mol-1) with Mn much larger than expected (10754 g
mol-1 for one chain per indium; 3585 for three chains).
Compound 17 gave well-controlled and faster ROP with
92% monomer conversion after 9 h (cf. 74% after 12 h for the
tris(alkyl)). The final Mn was in excellent agreement with one
PLA chain forming per In-OiPr moiety with a narrow PDI of
1.17. The gradient of the Mn vs conversion plot (SI, Figure
S7, 155(5) g mol-1 (% conversion)-1) was comparable within
catalyzed immortal ROP (“iROP”) of LA whereby n chains
of PLA are formed per metal center (n is the number of equiv
of alcohol, ROH, added).21 The PLA formed is of the type
RO-[PLA]-H with an alcohol-derived “RO” moiety forming
an end group. In contrast, there are few efficient ROP-based
routes to amine-terminated PLAs.22 These are desirable
targets since functionalized amines and poly(amines) are
readily available scaffolds for the preparation of complex
architectures such as block- or graft-copolymers, dendritic
copolymers, and star-shaped polymers.1h Metal amides
(L)M-NR2 are, as discussed above, nonideal initiators since
they are prone to poor molecular weight control and forma-
tion of macrocyclic polyesters.12b,23
We have recently introduced amine-co-initiated iROP as a
method for the efficient synthesis of amine-terminated PLA
using group 3 and lanthanide initiators.24 Sarazin and Carpen-
tier et al. have shown this can be extended to group 2 metals.25
Mechanistic studies24a have established the general mechanism
in eq 4 whereby a number of equivalents of LA are rapidly ring-
opened by a primary (or secondary) amine RNH2 (R is
typically Bn in most studies to date) via an activated monomer
process to form an amine-terminated alcohol 24, which then
acts as a chain transfer agent in the usual manner,21 eventually
forming amine-terminated PLA of the type RNH-[PLA]-H.
error to the ideal value of 144.1 g mol-1 (% conversion)-1
.
ROP of rac-LA in the Melt. Industrially, PLA is currently
produced in the melt.1d Kunioka and Hillmyer and Tolman
et al. have shown that both In(OTf)3 and InCl3 are active in
this regard.7a,e,f Table 8 summarizes the results with com-
plexes 14-16, 19, 21, and 23. Results for In(CH2SiMe3)3 and
In(CH2SiMe3)2(OiPr) (17) are again given for comparison.
Experiments were carried out with [rac-LA]0:[In] = 300:1 at
1
130 °C for 2 h, and the PLA was analyzed using H NMR
spectroscopy and GPC as above. All of the alkyl compounds
(entries 1-4 and 7) were active, again giving higher than
calculated Mn and PDIs between 1.39 and 3.22. In apparent
agreement with the solution phase experiments, the highest
conversions were found for 14, 23, and In(CH2SiMe3)3. The
amide compound 19 gave a lower conversion than expected
based on the solution kapp values but a reasonable agreement
between found and predicted Mn (23 250 vs 30 429 g mol-1
)
and a PDI of 1.36, which is respectable for melt polymeriza-
tions. The isopropoxide-“ate” compound 21 gave a much
lower Mn than expected, whereas In(CH2SiMe3)2(OiPr) (17)
gave the best overall performance, as judged by near-quan-
titative conversion, excellent agreement between found and
calculated Mn, and a reasonably narrow PDI for melt
conditions. Again all the PLAs formed were atactic.
Hillmyer and Tolman et al. found that the InCl3:BnOH:
Et3N system catalyzes the iROP of rac-LA when the
(22) (a) Coulembier, O.; Kiesewetter, M. K.; Mason, A.; Dubois, P.;
Hedrick, J. L.; Waymouth, R. M. Angew. Chem., Int. Ed. 2007, 46, 4719.
(b) Cai, Q.; Zhao, Y.; Bei, J.; Xi, F.; Wang, S. Biomacromolecules 2003,
2003, 828. (c) Kowalski, A.; Libiszowski, J.; Biela, T.; Cypryk, M.;
Duda, A.; Penczek, S. Macromolecules 2005, 38, 8170.
(23) Chisholm, M. H.; Delbridge, E. E. New J. Chem. 2003, 27, 1167.
(24) (a) Clark, L.; Cushion, M. G.; Dyer, H. D.; Schwarz, A. D.;
Duchateau, R.; Mountford, P. Chem. Commun. 2010, 46, 273. (b) Clark,
L.; Deacon, G. B.; Forsyth, C. M.; Junk, P. C.; Mountford, P.; Townley,
J. P. Dalton Trans. 2010, 39, 6693.
Amine-Co-initiated Immortal ROP. Alcohols are well-
known to function as chain transfer agents in the metal-
(21) (a) Amgoune, A.; Thomas, C. M.; Carpentier, J.-F. Macromol.
Rapid Commun. 2007, 28, 693. (b) Ajella, N.; Carpentier, J.-F.;
Guillaume, C.; Guillaume, S. G.; Helou, M.; Poirier, V.; Sarazin, Y.;
Trifonov, A. A. Dalton Trans. 2010, 39, 8363.
(25) Sarazin, Y.; Poirier, V.; Roisnel, T.; Carpentier, J.-F. Eur. J.
Inorg. Chem. 2010, 3423.

Article
Organometallics, Vol. 30, No. 5, 2011 1211
Table 9. ROP of rac-LA with Various Indium Compounds in the Presence of Co-initiatorsa
c
entry
system
temperature (°C) conversion (%)b time (h)
kapp
Mn (GPC)d Mn (calcd) Mw/Mn Pr
f
1
2
3
4
5
6
7
8
9
In(N2TsNpy)(CH2SiMe3) (14), 5 BnNH2
In(CH2SiMe3)3, 5 BnNH2
In(CH2SiMe3)3, 5 BnNH2
In(CH2SiMe3)3, 2 BnNH2
In(CH2SiMe3)2(OiPr) (17)
InCl3, 5 BnNH2, 2 Et3N
InCl3, 2 BnNH2, 2 Et3N
InCl3, 3 BnNH2
70
70
22
22
22
22
22
22
22
92
85
92
91
74
96
96
87
94
10
5
167
167
192
54
54
191
3
0.33(1)
1.11(2)
3310e
3765
2557
2759
6,665
10 725
2874
7025
6375
13 660
1.12
1.12
1.11
1.07
1.05
1.11
1.08
1.12
1.07
f
f
f
f
2510e
0.015(1)
0.015(1)
0.007(1)
0.068(7)
0.069(8)
0.012(1)
0.85(4)
3150e
7820e
11,800g
3,690e
7,560e
5,200h
13,130i
0.85
0.85
0.79
0.94
InCl3, BnOH, 2 Et3N
a Conditions: [rac-LA]0:[In] = 100:1, 4.0 mL of toluene at 70 °C (entries 1 and 2) or of CH2Cl2 at RT (entries 3-9), [rac-LA]0 = 1.00 M. Varying
equivalents of co-initiator and/or Brønsted base added as indicated. See Experimental Section for other details. b NMR conversion. c Apparent rate
constant with units h-1 or M-1 h-1 derived from the first- or second-order log plots, respectively (all systems were first-order with respect to rac-LA
except for entry 2; see the SI for further details). d Molecular weights (g mol-1) determined by GPC in THF at 30 °C using the appropriate
Mark-Houwink corrections. eAssuming one Bn-[LA]x-H chain for each equivalent of BnNH2 co-initiator present. f Atactic within experimental error.
gAssuming one iPrO-[LA]x-H chain formed per equivalent of 17. h Assuming two Bn-[LA]x-H chains formed per equivalent of InCl3. i Assuming one
BnO-[LA]x-H chain formed per equivalent of InCl3.
[InCl3]0:[BnOH]0 ratio was varied between 1:1 and 1:4.7e,f We
were interested to determine whether amine-co-initiated
iROP could be extended to indium. The results are summar-
ized in Table 9, and additional data are given in the SI
(Figures S8-S16).
an excess of iPrOH to In(CH2SiMe3)3 in C6D6 formed only
In(CH2SiMe3)2(OiPr) (17), the remaining alkyl groups being
unreactive. The good Mn control achieved in the presence of
BnNH2 again contrasts very favorably with the extremely
poor control found in the corresponding amine-free system
(Table 7, entry 7).
To make better comparisons with Hillmyer and Tolman
et al.’s directing ligand-free system (entry 9), we carried out a
series of further experiments in CH2Cl2 at RT. ROP using
In(CH2SiMe3)3 with 5 or 2 equiv of BnNH2 proceeded
extremely slowly (entries 3 and 4). The so-formed PLA had
final Mn values and Mn vs % conversion plots (Figures S10,
S11) consistent with five or two chains growing per indium
center, respectively. Consistent with the mechanism in eq 4,
the kapp values were identical even though [BnNH2]0 differed
by a factor of 2.5. Entry 5 and Figure S12 summarize the
ROP using In(CH2SiMe3)2(OiPr) (17) under these condi-
tions. One iPrO-terminated PLA chain was formed per equiv-
alent of 17. The similar kapp for 17 and the In(CH2SiMe3)3/
BnNH2 catalyst systems is consistent with the catalytic
model proposed.
In contrast to the InCl3-based catalyst, the amine-termi-
nated PLAs formed with all of the above systems are atactic.
Consistent with this, Hillymer and Tolman et al. found that
In(OCH2CH2OMe)3 also produces atactic PLA. Therefore,
as summarized in entries 6 and 7, we decided to use InCl3 and
Et3N in place of In(CH2SiMe3)3 in the presence of 5 or 2
equiv of BnNH2. This gave a 4-fold increase in kapp (again
independent of [BnNH2]0 as for entries 3 and 4) and formed
heterotactically enriched amine-terminated PLA with a Pr
value of 0.85 in each case. The experimental Mn values were
also in good agreement with those expected. However, the
kapp values were an order of magnitude smaller than the
Hillmyer and Tolman et al. system with InCl3:BnOH:Et3N
and may indicate the formation of an InCl(-[PLA]-
NHBn)2-type species (or likely a dimer of the same composi-
tion as proposed by Hillmyer and Tolman et al.)7f under the
amine-co-initiated iROP conditions. An induction period
was observed in each case, which was not present with the
In(CH2SiMe3)3-based system or the Hillmyer and Tolman
one. Excluding the Et3N from the systems and using InCl3 and
BnNH2 alone ([InCl3]:[BnNH2]0 = 1:3) gave heterotactic
PLA with a small decrease in Pr, but a substantial decrease in
kapp and increase in the induction period (see Figure S15).
Nonetheless, the PLA formed was amine-terminated and the
Mn values measured during the ROP were in reasonable
Polymerization of rac-LA in the presence of In(N2TsNpy)-
(CH2SiMe3) (14) and 5 equiv of BnNH2 ([rac-LA]0:[In]:-
[BnNH2]0 = 100:1:5) at 70 °C in toluene proceeded smoothly
to 92% completion after 10 h (entry 1, Table 9). The polymer
formed was identified as atactic BnNH-[PLA]-H by 1H
NMR and MALDI-ToF MS analysis.24a The Mn at comple-
tion (3310 g mol-1) was close to that expected (3765 g mol-1
)
for one chain growing per BnNH2 co-initiator and substan-
tially less than the 58 680 g mol-1 measured in the absence of
amine (Table 7, entry 1). The Mn vs % conversion plot
(Figure S8) was linear with a gradient of 34(3) g mol-1 (% con-
version)-1 (expected value 28.8 g mol-1 (% conversion)-1),
consistent with five BnNH-[PLA]-H chains growing in an
immortal manner. The rac-LA consumption followed first-
order kinetics.
NMR tube scale experiments in C6D6 found that 14 did
not undergo protonolysis with BnNH2 alone. However, in
the additional presence of rac-LA under conditions compar-
able those of the preparative-scale ROP experiment, con-
comitant formation of the protio-ligand H2N2TsNpy (10) was
observed, presumably due to the increased acidity of 24
relative to BnNH2. This suggests that the real catalyst in this
system is directing ligand-free and the supporting bis-
(sulfonamide)amine ligand has no direct role to play. Entries
2-8 of Table 9 summarize our further investigations of the
new indium-catalyzed amine-co-initiated iROP of rac-LA
using directing ligand-free initiators. Entry 9 is for Hillmyer
and Tolman et al.’s InCl3:BnOH:Et3N system (CH2Cl2, RT)
in our hands for comparison with entries 3-8 (the results are
effectively identical to those published7e,f).
Use of In(CH2SiMe3)3 with 5 equiv of BnNH2 ([rac-
LA]0:[In]:[BnNH2]0 = 100:1:5) at 70 °C in toluene also gave
atactic benzyl amine-terminated PLA with Mn values con-
sistent with one chain growing per amine added (entry 2 and
a linear Mn vs % conversion plot (Figure S9) with a gradient
of 28(2) g mol-1 (% conversion)-1). Model NMR tube scale
experiments in C6D6 showed the elimination of only one
equivalent of SiMe4 per tris(alkyl) initiator and indicated
that the propagating species in this system is of the type
In(CH2SiMe3)2(-[PLA]-NHBn) (or a dimer of the same
composition, cf. 17 and 18). Consistent with this, addition of

1212 Organometallics, Vol. 30, No. 5, 2011
Blake et al.
agreement with those expected for 2 chains per indium center
(i.e., with one of the BnNH2 acting as a Brønsted base in lieu
of Et3N).
steel MALDI target and left to dry. The spectra were recorded in
the refectron mode.
Polymer molecular weights (Mn, Mw) were determined by
GPC using a Polymer Laboratories Plgel Mixed-D column
(300 mm length, 7.5 mm diameter) and a Polymer Laboratories
PL-GPC50 Plus instrument equipped with a refractive index
detector. THF (HPLC grade) was used as an eluent at 30 °C
with a flow rate of 1 mL min-1. Linear polystyrenes were used as
primary calibration standards, and Mark-Houwink correc-
tions for poly(rac-LA) in THF were applied for the experimental
samples.19
Conclusion
Bis(sulfonamide)amine indium alkyl, bis(trimethylsilyl)-
amide, and “ate”-type isopropoxide compounds are readily
prepared and have been structurally characterized. They all
effect the ROP of rac-LA in solution at 70 °C or in the melt.
As expected for alkyl and amide initiators, the Mn control
achieved with 14-16, 19, and the bis(phenolate)amine 23
was poor because of an unfavorable mismatch between
initiation and propagation rates. The molecular weight con-
trol with the “ate” complex 21 was better, but the ROP was
slow, due the retention of LiCl in the initiator. The best-
behaved initiator in terms of living ROP was In-
(CH2SiMe3)2(OiPr) (17). When used alone, In(CH2SiMe3)3
is a very poor initiator, but in the presence of BnNH2 amine-
co-initiated immortal ROP occurs to give atactic amine-
terminated PLA in a controlled manner. Use of InCl3 and
Et3N in place of the indium alkyl gave a 4-fold increase in
activity and a substantial increase in heterotacticity. Initial
studies showed that BnNH2 and InCl3 alone could also
produce heterotactically enriched, amine-terminated PLA
at room temperature, albeit very slowly.
Starting Materials. In(CH2SiMe3)3,13b,c In{N(SiMe3)2}3,27
In(OtBu)3,28 H2N2TsNpy (10),9 H2N2TsNOMe (11),10 H2N2TsNPh
(12),8c and H2O2MeNpy (13) were synthesized according to
published procedures. Na2NTsNpy was prepared from 10 and
NaH (2.2 equiv) in THF according to a related procedure11 and
used without further purification. rac-LA was recrystallized
i
twice from toluene then sublimed twice prior to use. PrOH
was dried over freshly ground CaH2 and distilled before use.
InCl3 and In(OiPr)3 were purchased from Alfa Aesar and used
without further purification. All other materials were purchased
from Sigma Aldrich and used without further purification.
In(N2TsNpy)(CH2SiMe3) (14). To a solution of In(CH2SiMe3)3
(0.50 g, 1.33 mmol) in toluene (20 mL) was added dropwise a
solution of H2N2TsNpy (0.67 g, 1.33 mmol) in toluene (20 mL) at
RT. The red solution was heated to 70 °C, and this was
maintained for 16 h. Volatiles were removed under reduced
pressure to afford 14 as a yellow solid, which was washed with
pentane (3 ꢀ 10 mL) and dried in vacuo. Yield: 0.55 g (58%).
Diffraction-quality crystals were grown from a saturated to-
luene solution layered with pentane. 1H NMR (C6D6, 299.9
MHz): δ 8.74 (1H, d, 3J = 5.3 Hz, 2-NC5H4), 8.23 (4H, d, 3J =
8.2 Hz, 2-C6H4Me), 6.90 (4H, d, 3J = 7.6 Hz, 3-C6H4Me), 6.83
(1H, dd, 3J = 6.5 Hz, 8.2 Hz, 4-NC5H4), 6.53 (1H, dd, 3J = 5.3
Hz, 6.5 Hz, 3-NC5H4), 6.19 (1H, d, 3J = 7.6 Hz, 5-NC5H4), 3.08
(2H, m, CH2CH2NTs), 2.95 (2H, m, CH2CH2NTs) 2.84 (2H, s,
pyCH2N), 2.11 (2H, m, CH2CH2NTs), 1.99 (2H, m, CH2CH2
NTs) 1.93 (6H, s, C6H4Me), 0.92 (2H, s, CH2SiMe3), 0.12 (9H, s,
SiMe3). 13C{1H} NMR (C6D6, 75.5 MHz): δ 153.5 (6-NC5H4),
149.1 (2-NC5H4), 142.7 (4-C6H4Me), 141.2 (1-C6H4Me), 140.2
(4-NC5H4), 129.8 (3-C6H4Me), 128.9 (2-C6H4Me), 124.8 (5-
NC5H4), 124.5 (3-NC5H4), 58.2 (pyCH2), 56.8 (CH2CH2NTs),
42.0 (CH2CH2NTs), 21.5 (C6H4Me), 3.42 (SiMe3), 1.71 (CH2
SiMe3). EI-MS: m/z = 615 (100%), [M - CH2SiMe3]þ. IR
(NaCl plates, Nujol mull, cm-1): 1603 (m), 1276 (s), 1136 (s),
1086 (m), 1016 (m), 972 (m), 850 (m), 818 (m), 760 (w), 740 (w),
668 (m), 598 (w). Anal. Found (calcd for C28H39InN4O4S2Si): C,
47.79 (47.86); H, 5.55 (5.59), N, 7.92 (7.97).
Experimental Section
General Methods and Instrumentation. All manipulations
were carried out using standard Schlenk line or drybox tech-
niques under an atmosphere of argon or dinitrogen. Solvents
were degassed by sparging with dinitrogen and dried by passing
through a column of the appropriate drying agent.26 Toluene
was refluxed over sodium and distilled. Deuterated solvents
were dried over sodium (C6D6) or P2O5 (CDCl3 and CD2Cl2),
distilled under reduced pressure, and stored under dinitrogen in
Teflon valve ampules. NMR samples were prepared under
dinitrogen in 5 mm Wilmad 507-PP tubes fitted with J. Young
Teflon valves. 1H and 13C{1H} NMR spectra were recorded on a
Varian Mercury-VX 300 spectrometer at ambient temperature
unless stated otherwise and referenced internally to residual
protio-solvent (1H) or solvent (13C) resonances and are reported
relative to tetramethylsilane (δ = 0 ppm). Assignments were
1
confirmed using two-dimensional H-1H and 13C-1H NMR
In(N2TsNOMe)(CH2SiMe3) (15). To a solution of In(CH2Si
Me3)3 (0.50 g, 1.33 mmol) in toluene (20 mL) was added a
solution of H2N2TsNOMe (0.62 g, 1.33 mmol) in toluene (20 mL)
at RT. The yellow solution was heated to 70 °C, and this was
maintained for 16 h. Volatiles were removed under reduced
pressure to afford 15 as a yellow solid, which was washed with
pentane (3 ꢀ 10 mL) and dried in vacuo. Yield: 0.66 g (74%).
Diffraction-quality crystals were grown from a saturated toluene
solution layered with pentane. 1H NMR (C6D6, 299.9 MHz): δ
correlation experiments. Chemical shifts are quoted in δ (ppm)
and coupling constants in Hz. IR spectra were recorded on a
Nicolet Magna 560 ESP FTIR spectrometer. Samples were pre-
pared in a drybox as Nujol mulls between NaCl plates, and the data
are quoted in wavenumbers (cm-1). Elemental analyses were carried
out by the Elemental Analysis Service at the London Metropolitan
University and Elemental Microanalysis Ltd., Devon.
MALDI-ToF-MS analysis was performed on a Waters
MALDI micro equipped with a 337 nm nitrogen laser. An
accelerating voltage of 25 kV was applied. The polymer samples
were dissolved in THF at a concentration of 1 mg mL-1. The
cationization agent used was potassium trifluoroacetate (Fluka,
>99%) dissolved in THF at a concentration of 5 mg mL-1. The
matrix used was trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-pro-
penylidene]malononitrile (DCTB) (Fluka) and was dissolved in
THF at a concentration of 40 mg mL-1. Solutions of matrix,
salt, and polymer were mixed in a volume ratio of 4:1:4,
respectively. The mixed solution was hand-spotted on a stainless
3
3
8.14 (4H, d, J = 8.2 Hz, 2-C6H4Me), 6.89 (4H, J = 7.6 Hz,
3-C6H4Me), 3.28 (3H, s, OMe), 2.97 (2H, m, CH2CH2OMe),
2.82 (4H, overlapping 2m, CH2CH2NTs), 2.14 (2H, m, CH2
CH2OMe) 1.94 (6H, s, C6H4Me), 1.87 (4H, overlapping 2m,
CH2CH2NTs), 0.66 (2H, s, CH2SiMe3), 0.32 (9H, s, SiMe3).
13C{1H} NMR (C6D6, 75.5 MHz): δ 141.6 (4-C6H4Me), 141.5
(1-C6H4Me), 129.7 (3-C6H4Me), 128.1 (2-C6H4Me), 66.5 (CH2
CH2OMe), 59.5 (CH2CH2NTs), 57.7 (OMe), 57.2 (CH2CH2
€
(27) Burger, H.; Cichon, J.; Goetze, U.; Wannagat, U.; Wismar, H. J.
J. Organomet. Chem. 1971, 33, 1.
(28) Veity, M.; Hill, S.; Huch, V. Z. Anorg. Allg. Chem. 2001, 627,
(26) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
1495.

Article
Organometallics, Vol. 30, No. 5, 2011 1213
OMe), 42.7 (CH2NTs), 21.5 (C6H4Me), 3.07 (CH2SiMe3), 1.75
(SiMe3). EI-MS: m/z = 582 (100%), [M - CH2SiMe3]þ. IR
(NaCl plates, Nujol mull, cm-1): 1598 (w), 1299 (s), 1293 (s),
1259 (m), 1240 (w), 1199 (w), 1152 (s), 1136 (s), 1112 (m), 1091
(m), 984 (s), 976 (s), 922 (w), 860 (w), 826 (m), 812 (m), 744 (w),
668 (m). Anal. Found (calcd for C25H40InN3O5S2Si): C, 44.88
(44.84); H, 6.12 (6.02); N, 6.18 (6.28).
maintained for 48 h. Volatiles were partially removed under
reduced pressure to afford a pale brown suspension (∼5 mL). To
the suspension was added hexanes (10 mL), giving a beige
suspension. A beige solid was isolated via filtration, washed
with THF (2 ꢀ 5 mL), and dried in vacuo. The solid was
dissolved in CH2Cl2 (10 mL), then layered with hexanes (10
mL), yielding 19 as a white microcrystalline solid, which was
isolated and dried in vacuo. Yield: 0.54 g (68%). Diffraction-
quality crystals were grown from a saturated toluene solution
cooled to -30 °C. 1H NMR (CD2Cl2, 300.3 MHz): δ 9.14 (1H, d,
In(N2TsNPh)(CH2SiMe3) (16). To a solution of In(CH2Si
Me3)3 (0.50 g, 1.33 mmol) in toluene (20 mL) was added
dropwise a solution of H2N2TsNPh (0.67 g, 1.33 mmol) in toluene
(20 mL) at RT. The colorless solution was heated to 70 °C, and
this was maintained for 16 h. Volatiles were removed under
reduced pressure to afford 16 as a white solid, which was washed
with pentane (3 ꢀ 10 mL) and dried in vacuo. Yield: 0.75 g
(81%). 1H NMR (C6D6, 299.9 MHz): δ 8.23 (4H, d, 3J = 8.2 Hz,
2-C6H4Me), 7.03 (3H, overlapping 2m, 3-C6H5 and 4-C6H5),
6.92 (4H, d, 3J = 7.6 Hz, 3-C6H4Me), 6.65 (2H, d, 3J = 7.9 Hz,
2-C6H5), 3.30 (2H, s, PhCH2N), 3.08 (2H, m, CH2CH2NTs), 2.94
(2H, m, CH2CH2NTs), 2.02 (4H, overlapping 2m, CH2CH2NTs),
1.92 (6H, s, C6H4Me), 0.39 (9H, s, SiMe3) 0.30 (2H, s,
CH2SiMe3). 13C{1H} NMR (C6D6, 75.5 MHz): 142.1 (1-
C6H5), 140.6 (4-C6H4Me), 132.0 (1-C6H4Me), 131.7 (4-C6H5),
129.9 (2-C6H4Me), 129.2 (2-C6H5), 129.1 (3-C6H5), 128.3
(3-C6H4Me), 57.1 (PhCH2N), 51.0 (CH2CH2NTs), 40.8
(CH2CH2NTs), 21.5 (C6H4Me), 2.55 (SiMe3), 1.78 (CH2Si-
Me3). EI-MS: m/z = 614 (40%), [M - CH2SiMe3]þ. IR
(NaCl plates, Nujol mull, cm-1): 1599 (w), 1278 (s), 1148 (s),
1088 (m), 1020 (w), 983 (m), 834 (s), 766 (w), 709 (w), 668 (s), 600
(w). Anal. Found (calcd for C29H40InN3O4S2Si): C, 49.78
(49.64); H, 5.67 (5.75); N, 5.91 (5.99).
3
3J = 5.3 Hz, 2-NC5H4), 8.01 (1H, dd, J = 5.9 Hz, 7.6 Hz,
4-NC5H4), 7.76 (4H, d, 3J = 8.2 Hz, 2-C6H4Me), 7.61 (1H, dd,
3J = 5.9 Hz, 7.0 Hz, 3-NC5H4), 7.39 (1H, d, 3J = 7.6 Hz,
5-NC5H4), 7.23 (4H, d, 3J = 8.2 Hz, 3-C6H4Me), 4.00 (s,
pyCH2), 3.18 (2H, m, CH2CH2NTs), 2.94 (2H, m, CH2CH2NTs),
2.83 (4H, overlapping 2m, CH2CH2NTs), 2.37 (6H, s, C6H4Me),
0.06 (18H, s, SiMe3). 13C{1H} NMR (CD2Cl2, 75.5 MHz):
153.4 (6-NC5H4), 150.8 (2-NC5H4), 142.1 (4-C6H4Me), 141.5
(1-C6H4Me), 133.2 (4-NC5H4), 129.7 (3-C6H4Me), 127.4 (2-
C6H4Me), 125.1 (5-NC5H4), 125.0 (3-NC5H4), 58.6 (CH2
CH2NTs), 58.3 (pyCH2), 42.5 (CH2CH2NTs), 21.7 (C6H4Me),
5.77 (SiMe3). EI-MS: m/z = 615 (30%), [M - N(SiMe3)2]þ. IR
(NaCl plates, Nujol mull, cm-1): 1607 (m), 1281 (s), 1253 (m),
1137 (s), 1112 (m), 1067 (m), 1086 (m), 1020 (m), 937 (s), 903 (w),
883 (m), 858 (m), 811 (m), 763 (m), 723 (m), 663 (s). Anal. Found
(calcd for C30H46InN5O4S2Si2): C, 46.89 (46.44); H, 5.75 (5.98);
N, 8.57 (9.03).
In(N2TsNpy)(OiPr)Cl{Li(THF)} (21). To a solution of InCl3
(0.40 g, 1.83 mmol) in THF (20 mL) at -78 °C was added
dropwise a suspension of Na2NTsNpy (1.00 g, 1.83 mmol) in
THF (20 mL). The suspension was stirred at -78 °C for 1 h, then
allowed to warm to RT. To the suspension was added dropwise
a 1 M solution of LiOiPr (1.83 mL, 1.83 mmol) in hexanes at RT.
The resultant yellow solution was stirred at RT for 1 h. Volatiles
were removed under reduced pressure, and the resultant yellow
solid was dissolved in CH2Cl2 (20 mL). The solution was filtered
and concentrated under reduced pressure (∼5 mL), and hexanes
(20 mL) were added, giving a beige solid, which was isolated,
washed with hexanes (2 ꢀ 5 mL), and dried in vacuo. Crystal-
lization from THF (10 mL) at -30 °C gave 21 as a white
crystalline solid, which was isolated via filtration, washed with
THF at 0 °C (2 ꢀ 5 mL) and hexanes (2 ꢀ 5 mL), and then dried
in vacuo. Yield: 0.68 g (46%). Diffraction-quality crystals were
grown from a THF/hexanes solution cooled to 4 °C. 1H NMR
In(CH2SiMe3)2(OiPr) (17). To a solution of In(CH2SiMe3)3
(1.00 g, 2.66 mmol) in toluene (30 mL) at -78 °C was added
i
dropwise a solution of PrOH (0.20 μL, 2.66 mmol) in toluene
(30 mL) at -78 °C. The colorless solution was allowed to warm
to RT and was stirred for 3 h. Volatiles were removed under reduced
pressure to afford 17 as a colorless crystalline solid, which was
dried in vacuo. Yield: 0.84 g (95%). Diffraction-quality crystals
were grown from a saturated toluene solution. 1H NMR (C6D6,
299.9 MHz): δ 4.14 (1H, sept, 3J = 5.9 Hz, OCHMe2), 1.10 (6H,
d, 3J = 5.9 Hz, OCHMe2), 0.24 (18H, s, SiMe3), -0.10 (4H, s,
CH2SiMe3). 13C{1H} NMR (C6D6, 75.5 MHz): δ 66.9 (OCH
Me2), 29.0 (OCHMe2), 5.16 (CH2SiMe3), 3.10 (SiMe3). EI-MS:
m/z = 289 (95%), [M - OiPr]þ; 333 (30%), [M - Me]þ. IR
(NaCl plates, Nujol mull, cm-1): 1259 (s), 1246 (s), 1118 (m), 1093
(m), 1020 (m), 960 (m), 851 (m), 828 (s), 800 (m), 754 (w). Anal.
Found (calcd for C11H29InOSi2): C, 38.01 (37.93); H, 8.21 (8.39).
In(CH2SiMe3)2(OCH2CH2NMe2) (18). To a solution of In-
(CH2SiMe)3 (0.50 g, 1.33 mmol) in toluene (10 mL) at -78 °C
was added dropwise a solution of 2-(dimethylamino)ethanol
(0.12 g, 1.33 mmol) in toluene (20 mL). The solution was stirred
at -78 °C for 1 h, then allowed to warm to RT. The solution was
stirred at RT for 16 h, then concentrated under reduced pressure
and dried in vacuo to afford 18 as a colorless solid. Yield: 0.48 g
(96%). Diffraction-quality crystals were grown from a saturated
hexanes solution cooled to -78 °C. 1H NMR (C6D6, 299.9
MHz): δ 3.67 (2H, t, 3J = 5.57 Hz, OCH2CH2N), 2.05 (2H, t,
3J = 5.6 Hz, OCH2CH2N), 1.84 (6H, s, NMe2), 0.32
(18H, s, SiMe3), -0.38 (4H, s, SiCH2). 13C{1H} NMR (C6D6,
3
(CD2Cl2, 300.3 MHz): δ 8.00 (1H, d, J = 4.9 Hz, 2-NC5H4),
7.96 (2H, d, 3J = 8.2 Hz, 2-C6H4), 7.73 (1H, m, 4-NC5H4), 7.68
(2H, d, 3J = 8.2 Hz, 2-C6H4), 7.24 (2H, d, 3J = 8.2 Hz, 3-C6H4),
7.21 (1H, m, 3-NC5H4), 7.09 (2H, d, 3J = 8.2 Hz, 3-C6H4), 7.01
3
(1H, t, J = 7.0 Hz, 5-NC6H4), 4.52 (1H, m, OCHMe2), 3.72
(4H, overlapping 2m, OCH2CH2), 3.60 (1H, m, pyCH2),
3.32-2.77 (5H, overlapping 3m, pyCH2 and CH2CH2NTs),
2.45 (2H, m, CH2NTs), 2.36 (6H, s, C6H4Me), 1.82 (4H, over-
3
lapping 2m, OCH2CH2), 1.37 (3H, d, J = 6.2 Hz, OCHMe),
3
1.26 (3H, d, J = 6.2 Hz, OCHMe). 13C{1H} NMR (CD2Cl2,
75.5 MHz): δ 152.8 (6-NC5H4), 145.9 (2-NC5H4), 141.9 (4-
C6H4Me), 141.1 (1-C6H4Me), 140.0 (4-NC5H4), 129.5 (2-C6H4
Me), 129.1 (2-C6H4Me), 128.0 (3-C6H4Me), 127.2 (3-C6H4Me),
124.8 (5-NC5H4), 123.3 (3-NC5H4), 68.4 (OCH2CH2), 65.9
(OCHMe2), 61.6 (CH2CH2NTs), 55.5 (CH2CH2NTs), 42.2
(CH2CH2NTs), 40.9 (CH2CH2NTs), 28.0 (OCHMe), 27.6
(OCHMe), 26.1 (OCH2CH2), 21.7 (C6H4Me). EI-MS: m/z =
615 (20%), [In(N2TsNpy)]þ. IR (NaCl plates, Nujol mull, cm-1):
1603 (w), 1289 (m), 1270 (s), 1160 (s), 1146 (s), 1128 (m), 1090
(m), 1045 (w), 1023 (w), 995 (m), 977 (m), 921 (w), 834 (w), 814
(m), 767 (w), 668 (m), 604 (m). Anal. Found (calcd for
C11ClH43InLiN4O6S2): C, 46.87 (47.19); H, 5.32 (5.49); N,
6.84 (7.10).
75.5 MHz):
δ 63.2 (OCH2CH2N), 58.6 (OCH2CH2N),
45.5 (NMe2), 3.55 (SiMe3), 0.56 (SiCH2). EI-MS: m/z =
290 (100%), [M - CH2SiMe3]þ; 289 (70%), [M - OCH2-
CH2NMe2]þ. IR (NaCl plates, Nujol mull, cm-1): 1275 (m),
1255 (m), 1242 (s), 1183 (w), 1091 (s), 1033 (m), 970 (m), 949 (s),
889 (m), 857 (s), 824 (s), 753 (m), 681 (m), 668 (w). Anal. Found
(calcd for C12H32InNOSi2): C, 58.51 (58.33); H, 6.60 (6.47); N,
4.79 (4.86).
In(N2TsNpy){N(SiMe3)2} (19). To a solution of H2N2TsNpy
(0.51 g, 1.01 mmol) in toluene (10 mL) was added dropwise
a solution of In{N(SiMe3)2}3 (0.60 g, 1.01 mmol) in toluene
(10 mL) at RT. The solution was heated to 70 °C, and this was
In(N2TsNpy)Cl(py) (22). To a suspension of InCl3 (0.81 g,
3.66 mmol) in THF (20 mL) at -78 °C was added dropwise a
suspension of Na2N2TsNpy (2.00 g, 3.66 mmol) in THF (20 mL).

1214 Organometallics, Vol. 30, No. 5, 2011
Blake et al.
The suspension was stirred at -78 °C for 3 h, allowed to warm to
RT, and then stirred at RT for 16 h. Concentrating under
reduced pressure and drying in vacuo afforded a white solid.
The desired material was isolated by Soxhlet extraction into
pyridine (100 mL) over 48 h. The resultant yellow solution was
concentrated under reduced pressure to ∼15 mL and allowed to
stand at 4 °C for 1 h to afford 22 as a white solid, which was
isolated via filtration, washed with pyridine at 0 °C (5 mL), and
dried in vacuo. Yield: 1.11 g (47%). Diffraction-quality crystals
were grown from a saturated pyridine solution layered with
hexanes. Samples of 22 have a tendency to lose pyridine on
handling or exposure to vacuum. 1H NMR (C5D5N, 300.3
MHz): 8.92 (1H, d, J = 4.87 Hz, 2-NC5H4), 8.20 (4H, d, J
= 8.1 Hz, 2-C6H4), 7.72 (1H, 4-NC5H4), 7.21 (3H, 3 ꢀ over-
lapping m, 3,4,5-NC5H4), 7.10 (4H, d, 3J = 8.1 Hz, 3-C6H4Me),
4.16 (2H, m, pyCH2), 3.49 (2H, m, CH2CH2N2Ts), 3.16 (4H,
overlapping 2m, CH2CH2NTs and CH2CH2NTs), 2.93 (2H, m,
CH2CH2NTs), 2.17 (6H, s, C6H4Me). A 13C{1H} NMR spec-
trum could not be obtained due to the compound’s low solubi-
lity. EI-MS: m/z = 615 (100%), [M - Cl - py]þ. IR (NaCl
plates, Nujol mull, cm-1): 1606 (m), 1296 (s), 1279 (s), 1215 (w),
1142 (s), 1133 (s), 1109 (s), 1086 (m), 1003 (w), 979 (m), 952 (m),
917 (m), 834 (m), 808 (m), 769 (m), 756 (m), 698 (m), 673 (s), 633
resultant solution was heated at 70 °C and aliquots were taken at
the respective time. Upon completion of the reaction, wet THF
(10 mL) was added and the solution evaporated to dryness to
give the poly(rac-LA). Conversions were determined by 1H
NMR integration of the OCHMe resonance relative intensities
of the residual rac-LA and poly(rac-LA). A similar procedure
was used for the polymerization of rac-LA using in situ gener-
ated initiators. Where required, co-initiator was added immedi-
ately after the addition of CH2Cl2 (RT) or toluene (70 °C) to the
initiator and rac-LA. These polymerizations were carried out in
a glovebox under dinitrogen.
Procedure for Melt Polymerization of rac-LA. A Schlenk flask
was charged with initiator (13.9 mmol) and rac-LA (46.3 μmol)
and heated at 130 °C for 2 h with stirring. The mixture was cooled
to RT, wet THF (10 mL) was added, and the resulting solution
was evaporated to dryness to give the crude polymer.
3
3
Crystal Structure Determinations of In(N2TsNpy)(CH2SiMe3)
(14), In(N2TsNOMe)(CH2SiMe3) (15), In(CH2SiMe3)2(OiPr)
(17), In(CH2SiMe3)2(OCH2CH2NMe2) (18), In(N2TsNpy){N-
Ts
(SiMe3)2} (19), In(N2TsNpy)(OiPr)Cl{Li(THF)} (21), In(N2
Npy)Cl(py) (22), and In(O2MeNpy)(CH2SiMe3) (23). Crystal data
collection and processing parameters are given in Table S3 of the
SI. Crystals were mounted on glass fibers using perfluoropo-
lyether oil and cooled rapidly in a stream of cold N2 using an
Oxford Cryosystems Cryostream unit. Diffraction data were
measured using an Enraf-Nonius KappaCCD diffractometer.
As appropriate, absorption and decay corrections were applied
to the data and equivalent reflections merged.29 The structures
were solved with SIR92,30 and further refinements and all other
crystallographic calculations were performed using the CRYS-
TALS program suite.31 Other details of the structure solution
and refinements are given in the Supporting Information (CIF
data). A full listing of atomic coordinates, bond lengths and
angles, and displacement parameters for all the structures have
been deposited at the Cambridge Crystallographic Data Center.
See Guidelines for Authors, http://pubs.acs.org/JNP.
(w), 595 (w). Anal. Found (calcd for C24ClH28InN4O4S2 0.7
3
(C5H5N)): C, 46.59 (46.77); H, 4.57 (4.50); N, 9.32 (8.61).
In(O2MeNpy)(CH2SiMe3) (23). To a solution of In(CH2-
SiMe3)3 (0.50 g, 1.33 mmol) in toluene (10 mL) was added
dropwise a solution of H2O2MeNpy (0.50 g, 1.33 mmol) in
toluene (10 mL) at RT. The colorless solution was stirred at
RT for 16 h. The solution was filtered, and volatiles were
removed under reduced pressure to give 23 as a white solid,
which was washed with hexanes (2 ꢀ 5 mL) and dried in vacuo.
Yield: 0.50 g (65%). Diffraction-quality crystals were grown
from a saturated toluene solution layered with pentane. 1H
NMR (C6D6, 299.9 MHz): δ 7.87 (1H, d, 3J = 5.2 Hz,
2-NC5H4), 6.98 (2H, s, 4-C6H2Me2), 6.67 (1H, t, 3J = 6.3 Hz,
4-NC5H4), 6.51 (2H, s, 6-C6H2Me2), 6.27 (1H, m, 3J = 6.3 Hz,
3
Acknowledgment. We thank the EPSRC for support.
3-NC5H4), 6.01 (1H, d, J = 7.8 Hz, 5-NC5H4), 3.62 (2H, d,
2J = 12.4 Hz, NCH2Ar), 3.26 (2H, d, 2J = 12.4 Hz, NCH2Ar),
3.02 (2H, s, pyCH2N), 2.52 (6H, s, 3-C6H2Me2), 2.29 (6H, s,
5-C6H2Me2), 0.62 (9H, s, SiMe3), 0.22 (2H, s, CH2SiMe3).
13C{1H} NMR (C6D6, 75.5 MHz): δ 161.7 (6-C5H4N), 154.3
(2-C6H2Me2), 146.5 (2-C6H4N), 139.0 (4-C6H4N), 132.5 (4-C6
H2Me2), 129.1 (6-C6H2Me2), 128.5 (5-C6H2Me2), 123.5 (3-C6H2
Me2), 123.2 (5-NC5H4), 123.2 (3-NC5H4), 120.4 (1-C6H2Me2),
61.1 (NCH2Ar), 59.2 (pyCH2N), 20.8 (5-C6H2Me2), 17.9 (3-C6
H2Me2), 2.89 SiMe3), -0.67 (CH2SiMe3). EI-MS: m/z = 576
(100%), [M]þ. IR (NaCl plates, Nujol mull, cm-1): 1605 (s),
1347 (w), 1310 (m), 1245 (m), 1218 (m), 1161 (s), 1084 (m), 1017
(m), 968 (s), 858 (s), 835 (m), 805 (m), 792 (m), 760 (s), 692 (m),
668 (w), 643 (w). Anal. Found (calcd for C28InH37N2O2Si): C,
38.13 (38.19); H, 8.53 (8.55); N, 3.71 (3.66).
Supporting Information Available: X-ray crystallographic
data in CIF format for the structure determinations of In-
(N2TsNpy)(CH2SiMe3) (14), In(N2TsNOMe)(CH2SiMe3) (15), In-
(CH2SiMe3)2(OiPr) (17), In(CH2SiMe3)2(OCH2CH2NMe2)
(18), In(N2TsNpy){N(SiMe3)2} (19), In(N2TsNpy)(OiPr)Cl{Li-
(THF)} (21), In(N2TsNpy)Cl(py) (22), and In(O2MeNpy)(CH2-
SiMe3) (23), plots of the molecular structures of 17 and 18, and
associated selected distances and angles. Additional data con-
cerning the ROP catalysis (Mn and Mw/Mn vs % conversion; %
conversion vs time; first- or second-order log plots for rac-LA
consumption). This information is available free of charge via
the Internet at http://pubs.acs.org.
(29) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode; Academic Press: New York, 1997.
(30) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27,
435.
General Procedure for Solution Polymerization of rac-LA. rac-
LA (4.00 mmol) and initiator (0.04 mmol) were added to an
ampule fitted with a J. Young Teflon valve and heated to 70 °C.
To this was added hot (70 °C) toluene (4.0 mL) or RT (22 ( 2 °C)
CH2Cl2 (4.0 mL), rapidly dissolving both materials. Where co-
initiator was required, this was added immediately after. The
(31) Betteridge, P. W.; Cooper, J. R.; Cooper, R. I.; Prout, K.;
Watkin, D. J. J. Appl. Crystallogr. 2003, 36, 1487.