Sulfonamide-supported group 4 catalysts for the ring-opening polymerization of ε-caprolactone and rac-lactide

Article abstract of DOI:10.1021/ic901524s

Reaction of RCH₂N(CH₂CH₂NHSO ₂TOI)₂ (R=2-NC₅H₄ (8, H ₂L^py) or MeOCH₂ (9, H₂L ^OMe)) with Ti(NMe₂)₄ at

Full text of DOI:10.1021/ic901524s

10442 Inorg. Chem. 2009, 48, 10442–10454
DOI: 10.1021/ic901524s
Sulfonamide-Supported Group 4 Catalysts for the Ring-Opening Polymerization of
ε-Caprolactone and rac-Lactide
Andrew D. Schwarz, Amber L. Thompson, and Philip Mountford*
Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K.
Received July 31, 2009
Reaction of RCH2N(CH2CH2NHSO2Tol)2 (R=2-NC5H4 (8, H2Lpy) or MeOCH2 (9, H2LOMe)) with Ti(NMe2)4 at room
temperature afforded Ti(Lpy)(NMe2)2 (10) or Ti(LOMe)(NMe2)2 (11), respectively, which contain tetradentate
bis(sulfonamide)amine ligands. The corresponding reactions with Ti(OiPr)4 or Zr(OiPr)4 HOiPr required more forcing
3
conditions to form the homologous bis(isopropoxide) analogues, M(LR)(OiPr)2 (M=Ti, R=py (12) or OMe (14); M=Zr,
R=py (13) or OMe (15)). Reaction of Ti(NMe2)2(OiPr)2 with H2LR formed 12 or 14 under milder conditions. The X-ray
structures of 10-15 have been determined revealing Cs symmetric, 6-coordinate complexes except for 13 which is
7-coordinate with one κ2(N,O) bound sulfonamide donor. Compounds 10- 15 are all catalysts for the ring-opening
polymerization (ROP) of ε-caprolactone, with the isopropoxide compounds being the fastest and best controlled,
especially in the case of zirconium. In addition, Zr(LOMe)(OiPr) 2 (15) was an efficient catalyst for the well-controlled
ROP of rac-lactide both in toluene at 100 °C and in the melt at 130 °C, giving atactic poly(rac-lactide). The
polymerization rates and control achieved for 13 and 15 are comparable to those of the well-established
bis(phenolate)amine-supported Group 4 systems reported recently.
Introduction
typically magnesium,12-15 zinc,12,14,16-19 calcium,15,20,21
aluminum,19,22-25 yttrium,26,27 the lanthanides,28-30 tin,31
Group 4 elements,19,32-38 and iron.39,40 They generally feature
one or more alkoxide functional (initiating) groups, and are
supported by a polydentate ancillary ligand which effects
control of the catalyst nuclearity and coordination-insertion
chain growth mechanism.
There is much current interest in the controlled ring-
opening polymerization (ROP) of cyclic esters such as ε-
caprolactone (ε-CL) and rac-lactide (rac-LA) because of the
biocompatibility and biodegradability of the resulting polye-
sters. These polymers can act as replacements for oil-based
materials and can be derived from 100% renewable resources
including corn and sugar beet.1-7 Metal-based catalysts
for the ROP of cyclic esters have been extensively re-
viewed.8-11 They can be derived from a variety of Lewis acids,
*To whom correspondence should be addressed. E-mail: philip.mountford@
chem.ox.ac.uk.
(1) Emo, C.; Roberto, S. Adv. Mater. 1996, 8, 305–313.
(2) Uhrich, K. E.; Cannizzaro, S. M.; Langer, R. S.; Shakesheff, K. M.
Chem. Rev. 1999, 99, 3181–3198.
(3) Drumright, R. E.; Gruber, P. R.; Henton, D. E. Adv. Mater. 2000, 12,
1841–1846.
(4) Yoshito, I.; Hideto, T. Macromol. Rapid Commun. 2000, 21, 117–132.
(5) Stefan, M. Angew. Chem., Int. Ed. 2004, 43, 1078–1085.
(6) Williams, C. K.; Hillmyer, M. A. Polym. Rev. 2008, 48, 1–10.
(7) Place, E. S.; George, J. H.; Williams, C. K.; Stevens, M. M. Chem. Soc.
Rev. 2009, 38, 1139–1151.
Among the transition metals, Group 4 complexes have
exhibited very good control of the polymerization process,
(13) Chisholm, M. H.; Eilerts, N. W. Chem. Commun. 1996, 853–854.
(14) Chisholm, M. H.; Huffman, J. C.; Phomphrai, K. J. Chem. Soc.,
Dalton Trans. 2001, 222–224.
(8) Dechy-Cabaret, O.; Martin-Vaca, B.; Bourissou, D. Chem. Rev. 2004,
104, 6147–6176.
(9) O’Keefe, B. J.; Hillmyer, M. A.; Tolman, W. B. J. Chem. Soc., Dalton
Trans. 2001, 2215–2224.
(10) Platel, R. H.; Hodgson, L. M.; Williams, C. K. Polym. Rev. 2008, 48,
11–63.
(15) Wheaton, C. A.; Hayes, P. G.; Ireland, B. J. Dalton Trans. 2009,
4832–4846.
(16) Cheng, M.; Attygalle, A. B.; Lobkovsky, E. B.; Coates, G. W. J. Am.
Chem. Soc. 1999, 121, 11583–11584.
(11) Kamber, N. E.; Jeong, W.; Waymouth, R. M.; Pratt, R. C.;
Lohmeijer, B. G. G.; Hedrick, J. L. Chem. Rev. 2007, 107, 5813–5840.
(12) Chamberlain, B. M.; Cheng, M.; Moore, D. R.; Ovitt, T. M.;
Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 3229–3238.
(17) Chisholm, M. H.; Eilerts, N. W.; Huffman, J. C.; Iyer, S. S.; Pacold,
M.; Phomphrai, K. J. Am. Chem. Soc. 2000, 122, 11845–11854.
(18) Wheaton, C. A.; Ireland, B. J.; Hayes, P. G. Organometallics 2009,
28, 1282–1285.
r
pubs.acs.org/IC
Published on Web 09/28/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 21, 2009 10443
featuring reasonably fast initiation and minimal side reac-
tions (chain transfer). This leads to polymers of well-defined
and predictable molecular weights (Mn), narrow polydisper-
sity indices (PDIs), and (for rac-LA) heterotactic enrich-
ment.32,41,42 Early work32 with these metals was based
around simple homoleptic metal alkoxides M(OR)4 (R =
alkyl; M=Ti or Zr),32,43 which operate as ROP catalysts via a
coordination-insertion mechanism. Aida et al. employed
bidentate bis(phenolate) ancillary ligands on titanium with
isopropoxide initiating groups, obtaining poly(ε-CL) with
narrow PDI (ca. 1.2) (1 in Figure 1).44,45 Subsequent work by
Verkade et al. employed titanatranes of various structures
featuring either bulky aryloxide or isopropoxide initiating
groups.33,46-48 Concurrent with these developments, Harada
et al. reported bulky bidentate and tridentate phenolate
complexes of titanium bearing isopropoxide and diethylami-
do initiator groups. These species demonstrated moderate
activities and control for polymerization of ε-CL and LA in
toluene at elevated temperatures.49,50 Gibson and Long used
aminophenoxide ligands bound to titanium for the polymer-
ization of LA in toluene at 70 °C and obtained poly(LA) of
narrow PDI (1.1-1.2) with good activity (e.g., 96% conver-
sion after 6 h). However, where rac-LA was employed, no
significant control over polymer tacticity was obtained.51,52
Interestingly, upon employing complex 2 (Figure 1) it was
possible to moderate catalyst activity by redox control of the
ferrocenyl groups on the ligand periphery.53 Significant ad-
vances have been achieved recently using tetradentate bis-
(phenolate)diamine and related ancillary ligands such as in 3
and 4 (Figure 1).41,42,54-57 Good control has also been
achieved for the ROP of rac-LA under industrially desirable
melt conditions. C3-symmetric zirconium tris(phenolate)-
amine isopropoxide complexes of the type 4 (Figure 1) act
as well-controlled single site catalysts that give both narrow
PDIs and highly heterotactically enriched poly(rac-LA).54
We have recently been interested to develop new support-
ing ligands for Group 4 ROP catalysts and speculated that
polydentate sulfonamides (containing -N(R)SO2R0 func-
tional groups) could be useful in this regard. The electron-
withdrawing SO2R0 moieties reduce the normal basicity of
anionic amide donors “NR2” and might therefore allow them
to act as phenolate mimics. Although N(R)SO2R0 based
ligands lack the steric control afforded by bulky ring-sub-
stituted phenolates OAr (e.g., 3 and 4 in Figure 1), the well-
established ability of sulfonamide ligands to adopt κ2(N,O)
coordination modes58-68 could confer additional stability on
(19) Chisholm, M. H.; Lin, C.-C.; Gallucci, J. C.; Ko, B.-T. Dalton Trans.
2003, 406–412.
(20) Zhong, Z.; Dijkstra, P. J.; Birg, C.; Westerhausen, M.; Feijen, J.
Macromolecules 2001, 34, 3863–3868.
(21) Antelmann, B.; Chisholm, M. H.; Iyer, S. S.; Huffman, J. C.;
Navarro-Llobet, D.; Pagel, M.; Simonsick, W. J.; Zhong, W. Macromole-
cules 2001, 34, 3159–3175.
(22) Dubois, P.; Jerome, R.; Teyssie, P. Macromolecules 1991, 24, 977–
981.
(23) Kowalski, A.; Duda, A.; Penczek, S. Macromolecules 1998, 31, 2114–2122.
(24) Aida, T.; Inoue, S. Acc. Chem. Res. 1996, 29, 39–48.
(25) Cameron, P. A.; Jhurry, D.; Gibson, V. C.; White, A. J. P.; Williams,
D. J.; Williams, S. Macromol. Rapid Commun. 1999, 20, 616–618.
(26) McLain, S. J.; Ford, T. M.; Drysdale, N. E. Polym. Prepr. (Am.
Chem. Soc., Div. Polym. Chem.) 1992, 33, 463.
(27) Chamberlain, B. M.; Sun, Y.; Hagadorn, J. R.; Hemmesch, E. W.;
Young, V. G., Jr; Hillmyer, M. A.; Tolman, W. B. Macromolecules 1999, 32,
2400–2402.
(28) Giesbrecht, G. R.; Whitener, G. D.; Arnold, J. J. Chem. Soc., Dalton
Trans. 2001, 923–927.
(29) Dyer, H. E.; Huijser, S.; Schwarz, A. D.; Wang, C.; Duchateau, R.;
Mountford, P. Dalton Trans. 2008, 32–35.
(30) Bonnet, F.; Cowley, A. R.; Mountford, P. Inorg. Chem. 2005, 44,
9046–9055.
(31) Kricheldorf, H. R.; Kreiser-Saunders, I.; Boettcher, C. Polymer 1995,
36, 1253–1259.
(32) Kricheldorf, H. R.; Berl, M.; Scharnagl, N. Macromolecules 1988, 21,
286–293.
(33) Kim, Y.; Jnaneshwara, G. K.; Verkade, J. G. Inorg. Chem. 2003, 42,
1437–1447.
(34) Thomas, D.; Arndt, P.; Peulecke, N.; Spannenberg, A.; Kempe, R.;
Rosenthal, U. Eur. J. Inorg. Chem. 1998, 1998, 1351–1357.
(35) Dobrzynski, P.; Li, S.; Kasperczyk, J.; Bero, M.; Gasc, F.; Vert, M.
Biomacromolecules 2005, 6, 483–488.
(36) Mogstad, A.-L.; Waymouth, R. M. Macromolecules 1994, 27, 2313–
2315.
(37) Miola Delaite, C.; Hamaide, T.; Spitz, R. Macromol. Chem. Phys.
1999, 200, 1771–1778.
(38) Hsieh, K. C.; Lee, W. Y.; Hsueh, L. F.; Lee, H. M.; Huang, J. H. Eur.
J. Inorg. Chem. 2006, 2306–2312.
(49) Takashima, Y.; Nakayama, Y.; Watanabe, K.; Itono, T.; Ueyama,
N.; Nakamura, A.; Yasuda, H.; Harada, A.; Okuda, J. Macromolecules
2002, 35, 7538–7544.
(50) Takashima, Y.; Nakayama, Y.; Hirao, T.; Yasuda, H.; Harada, A. J.
Organomet. Chem. 2004, 689, 612–619.
(51) Atkinson, R. C. J.; Gerry, K.; Gibson, V. C.; Long, N. J.; Marshall,
E. L.; West, L. J. Organometallics 2006, 26, 316–320.
(52) Gregson, C. K. A.; Blackmore, I. J.; Gibson, V. C.; Long, N. J.;
Marshall, E. L.; White, A. J. P. Dalton Trans. 2006, 3134–3140.
(53) Gregson, C. K. A.; Gibson, V. C.; Long, N. J.; Marshall, E. L.;
Oxford, P. J.; White, A. J. P. J. Am. Chem. Soc. 2006, 128, 7410–7411.
(54) Chmura, A. J.; Davidson, M. G.; Frankis, C. J.; Jones, M. D.; Lunn,
M. D. Chem. Commun. 2008, 1293–1295.
(55) Sarazin, Y.; Howard, R. H.; Hughes, D. L.; Humphrey, S. M.;
Bochmann, M. Dalton Trans. 2006, 340–350.
(56) Chmura, A. J.; Cousins, D. M.; Davidson, M. G.; Jones, M. D.;
Lunn, M. D.; Mahon, M. F. Dalton Trans. 2008, 1437–1443.
(57) 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, 7250–7257.
(58) Armistead, L. T.; White, P. S.; Gagne, M. R. Organometallics 1998,
17, 216–220.
(59) Armistead, L. T.; White, P. S.; Gagne, M. R. Organometallics 1998,
17, 4232–4239.
(60) Pritchett, S.; Gantzel, P.; Walsh, P. J. Organometallics 1997, 16,
5130–5132.
(61) Pritchett, S.; Woodmansee, D. H.; Gantzel, P.; Walsh, P. J. J. Am.
Chem. Soc. 1998, 120, 6423–6424.
(62) Pritchett, S.; Gantzel, P.; Walsh, P. J. Organometallics 1999, 18, 823–
831.
(63) Lensink, C.; Gainsford, G. J.; Baxter, N. I. Acta Crystallogr., Sect. C:
Cryst. Struct, Commun. 2001, 57, 366–367.
(64) Lensink, C.; Gainsford, G. J.; Baxter, N. I. Acta Crystallogr., Sect. C:
Cryst. Struct, Commun. 2001, 57, 368–369.
(65) Hamura, S.; Oda, T.; Shimizu, Y.; Matsubara, K.; Nagashima, H. J.
Chem. Soc., Dalton Trans. 2002, 1521–1527.
(39) O’Keefe, B. J.; Monnier, S. M.; Hillmyer, M. A.; Tolman, W. B. J.
Am. Chem. Soc. 2001, 123, 339–340.
(40) O’Keefe, B. J.; Breyfogle, L. E.; Hillmyer, M. A.; Tolman, W. B. J.
Am. Chem. Soc. 2002, 124, 4384–4393.
(41) Gendler, S.; Segal, S.; Goldberg, I.; Goldschmidt, Z.; Kol, M. Inorg.
Chem. 2006, 45, 4783–4790.
(42) Chmura, A. J.; Davidson, M. G.; Jones, M. D.; Lunn, M. D.; Mahon,
M. F. Dalton Trans. 2006, 887–889.
(43) Cayuela, J.; Bounor-Legare, V.; Cassagnau, P.; Michel, A. Macro-
molecules 2006, 39, 1338–1346.
(44) Takeuchi, D.; Nakamura, T.; Aida, T. Macromolecules 2000, 33,
725–729.
(66) Ackermann, L.; Bergman, R. G.; Loy, R. N. J. Am. Chem. Soc. 2003,
125, 11956–11963.
´
(67) Costa, A. M.; Garcıa, C.; Carroll, P. J.; Walsh, P. J. Tetrahedron
(45) Takeuchi, D.; Aida, T. Macromolecules 2000, 33, 4607–4609.
(46) Kim, Y.; Verkade, J. G. Organometallics 2002, 21, 2395–2399.
(47) Youngjo, K.; John, G. V. Macromol. Rapid Commun. 2002, 23, 917–
921.
2005, 61, 6442–6446.
(68) Massimiliano, F.; Fredrik, L.; Myriam Mba, B.; Patrick, R.; Marco,
C.; Lutz, H. G.; Giulia, L.; Christina, M. Eur. J. Inorg. Chem. 2006, 2006,
1032–1040.
(48) Youngjo, K.; John, G. V. Macromol. Symp. 2005, 224, 105–118.

10444 Inorganic Chemistry, Vol. 48, No. 21, 2009
Schwarz et al.
Figure 1. Examples of Group 4 catalysts for the ROP of cyclic esters.41,42,44,45,53,54
Figure 2. Examples of a recent aluminum ROP catalyst69 and selected Group 4 sulfonamide compounds.60,65,66
otherwise unsaturated metal centers. Sulfonamides in general
are attractive synthetic targets because of their relatively
simple preparation from the corresponding sulfonyl chlor-
ides, a wide range of which are commercially available. There
have been only two reports of sulfonamide-supported ROP
catalysts to date, in both cases for aluminum (e.g., complex 5,
Figure 2).69,70 Although 5 is a very slow catalyst for the ROP
In this contribution we report the synthesis and structures
of a series of new titanium and zirconium complexes derived
from the N4-donor sulfonamide (2-NC5H4)CH2N-
(CH2CH2NHSO2Tol)2 (8, H2Lpy) and the related N3O-
donor MeOCH2CH2N(CH2CH2NHSO2Tol)2 (9, H2LOMe
)
together with their performance as ROP catalysts for ε-CL
and rac-LA.
of L-lactide, the polymerization was well-controlled suggest-
ing that sulfonamide complexes of Group 4 metals (which
show higher intrisic activities compared with aluminum)
would be appropriate targets. A number of Group 4 (in
particular titanium) complexes of certain bi- and tridentate
bis(sulfonamide) ligands have been reported over the past 10
years (see Figure 2 for examples) and are effective for a
variety of catalytic transformations such as synthesis of
acetylenic alcohols,71 enantioselective addition of diethyl
zinc to benzaldehyde,62,72 hydroamination of alkynes and
allenes,66 and Zeigler-Natta catalysis.73 Some selected
examples are given in Figure 2.61,72 To date, no Group 4
sulfonamide compounds have been evaluated as catalysts for
ROP.
Results and Discussion
Synthesis. The known74,75 protio-ligands H2Lpy (8) and
H2LOMe (9) were synthesized in high yield by ring-open-
ing reactions of N-tosyl aziridine with the appropriate
amine, namely, 2-NC5H4CH2NH2 or MeOCH2CH2NH2,
respectively. Although the solid state structure of 8
has been previously described, that of 9 has not been
(69) Wu, J.; Pan, X.; Tang, N.; Lin, C.-C. Eur. Polym. J. 2007, 43, 5040–
5046.
(70) Zhao, J.; Song, H.; Cui, C. Organometallics 2007, 26, 1947–1954.
::
(71) Lutjens, H.; Nowotny, S.; Knochel, P. Tetrahedron: Asymmetry
1995, 6, 2675–2678.
(72) Cheng, G.; Jun, Q.; Zhang, X.; Verdugo, D.; Larter, M. L.; Christie,
R.; Kenney, P.; Walsh, P. J. Tetrahedron 1997, 53, 4145–4158.
(73) Padmanabhan, S.; Govindarajan, S. J. Polym. Sci., Part A: Polym.
Chem. 2006, 44, 4006–4014.
(74) Skinner, M. E. G.; Li, Y.; Mountford, P. Inorg. Chem. 2002, 41,
1110–1119.
(75) Bailey, N. A.; Fenton, D. E.; Hellier, P. C.; Hempstead, P. D.;
Casellatob, U.; Vigatob, P. A. Dalton Trans. 1992, 2809–2816.

Article
Inorganic Chemistry, Vol. 48, No. 21, 2009 10445
Scheme 1. Synthesis of the New Complexes 10-15
Figure 3. Displacement ellipsoid plot of H2LOMe (9). C-bound H atoms
are omitted for clarity, H(1) and H(2) are drawn as spheres of arbitrary
radius, and the ellipsoids are drawn at the 20% probability level.
Table 1. Selected Bond Distances (A) and Angles (deg) for H2LOMe (9)
N(1)-S(1)
N(2)-S(2)
S(1)-O(2)
S(1)-O(3)
S(2)-O(4)
1.618(2)
1.602(2)
1.433(2)
1.432(2)
1.434(2)
168(3)
S(2)-O(5)
N(1)-H(1)
N(2)-H(2)
1.432(2)
0.83(3)
0.92(3)
2.20(4)
2.53(4)
106(2)
111(2)
121.3(2)
120(2)
115(2)
H(1) O(1)
3 3 3
H(2) O(1)
3 3 3
N(1)-H(1) O(1)
S(1)-N(1)-H(1)
H(1)-N(1)-C(5)
S(2)-N(2)-C(7)
S(2)-N(2)-H(2)
H(2)-N(2)-C(7)
3 3 3
N(2)-H(2) O(1)
155(3)
3 3 3
C(3)-O(1)-C(2)
112.2(2)
131.0(9)
105.6(8)
118.84(18)
C(3)-O(1) H(1)
3 3 3
3 3 3
C(3)-O(1) H(2)
S(1)-N(1)-C(5)
reported. Therefore, for comparison with its metal com-
plexes described below, the X-ray structure of 9 was
determined. The molecular structure is shown in Figure 3
and selected distances and angles are listed in Table 1.
Molecules of H2LOMe possess two intramolecular
N-H O hydrogen bonds between the two sulfonamide
3 3 3
nitrogens and the OMe group oxygen atom. This pre-
organizes 9 into a geometry akin to that required to bind a
metal center. All bond lengths and angles for 9 lie within
the expected ranges for compounds of this type.76 Protio-
ligand H2Lpy (8) also crystallized in a pre-organized
manner, but in that case an EtOH molecule of crystal-
lization was incorporated into the ligand cavity through
multiple H-bonding interactions.74
As described below, these bis(dimethylamide) com-
pounds were poor catalysts for the ROP of ε-CL and
rac-LA, and so we focused our further efforts on their
bis(isopropoxide) homologues, M(Lpy)(OiPr)2 (M = Ti
(12) or Zr (13)) and M(LOMe)(OiPr)2 (M=Ti (14) or Zr
(15)) (Scheme 1). Attempted stoichiometric reaction of
H2Lpy (8) with Ti(OiPr)4 did not proceed at any appreci-
able rate at ambient temperature, presumably reflecting
the reduced basicity of isopropoxide compared to di-
methylamide in the respective titanium starting materials.
Nonetheless, heating 8 with an excess of Ti(OiPr)4 in
toluene for 16 h gave good yields of 12 after recrystalliza-
tion. The zirconium congener 13 was prepared in 42%
recrystallized yield in an analogous fashion using an
Protonolysis reactions of 8 or 9 with 1 equiv of Ti-
(NMe2)4 in benzene at ambient temperature gave the
bis(dimethylamide) complexes Ti(Lpy)(NMe2)2 (10) and
Ti(LOMe)(NMe2)2 (11), respectively, in 50-55% yield
after recrystallization (Scheme 1). When followed in
CD2Cl2 on the NMR tube scale the yields were effectively
quantitative and the expected HNMe2 side product was
observed. The solid state structures of both compounds
have been determined (vide infra) and confirm those
shown in Scheme 1. The solution NMR spectra at 303
K (for 10) or ambient temperature (for 11) are also
consistent with the Cs symmetric solid state structures.
However, cooling the NMR samples of 10 to ambient
temperature or below led to considerable broadening of
the resonances and then the appearance of multiple ligand
environments. This suggests that several different isomers
may exist in solution, perhaps involving C1 and Cs
symmetry (cf. certain bis(phenolate) complexes)77 and/
or additional intra- and/or intermolecular coordination
of the tosyl group oxygen atoms as discussed below and
noted elsewhere (cf. Figure 2, compound 6).60-62,66
excess of Zr(iOPr)4 HOiPr. However, the LOMe-substi-
3
tuted analogues 14 and 15 could not be obtained by the
solution reaction of H2LOMe, even when using large
excesses of Ti(OiPr)4 or Zr(iOPr)4 HOiPr and extended
3
reaction times. This highlights the equilibrium nature of
these alcohol-elimination reactions and the apparent
need for a strong σ-donor to aid complexation to the
metal. Compounds 14 and 15 were eventually prepared
using melt conditions at 125-130 °C for 4-5 h under a
dynamic partial pressure to remove the eliminated iPrOH.
Recrystallization afforded the pure complexes in about
45% yield. As for 10, the NMR spectra of the zirconium
complexes showed evidence of complex solution state
dynamic behavior. The molecular structures of all four
complexes 12- 15 were therefore determined (vide infra)
and again support the structures depicted in Scheme 1.
(76) Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J. Chem. Inf. Comput.
Sci. 1996, 36, 746 (The United Kingdom Chemical Database Service).
(77) Toupance, T.; Dubberley, S. R.; Rees, N. H.; Tyrrell, B. R.;
Mountford, P. Organometallics 2002, 21, 1367–1382.

10446 Inorganic Chemistry, Vol. 48, No. 21, 2009
Schwarz et al.
Figure 4. (a) Displacement ellipsoid plot of Ti(Lpy)(NMe2)2 (10). (b) Displacement ellipsoid plot of Ti(LOMe)(NMe2)2 (11) where atoms carrying the suffix
“A” are related to their counterparts by the symmetry operator -x, y, -z þ 3/2. Ellipsoids are drawn at the 20% probablility level. H atoms and benzene
molecules of crystallization and elements of disorder (for 11) are omitted for clarity.
As shown in eq 1, Ti(Lpy)(OiPr)2 (12) and Ti(LOMe)-
(OiPr)2 (14) could also be prepared from Ti(NMe2)2(OiPr)2
and 1 equiv of the respective protio-ligand. No evidence for
the formation of the bis(dimethylamide) complexes 10 or 11
was found in either case. Compound 14 was isolated in
78% yield on the preparative scale after 2 h reaction time.
An NMR tube scale reaction showed quantitative formation
of 12 for the corresponding reaction with H2Lpy (8).
compared with that of OiPr. Consistent with previous
structural studies, the average Ti-NMe2 distance of
1.909 A in 10 and 11 is substantially shorter than the
average Ti-NTs distance, due mainly to the electron-
withdrawing nature of the -SO2Tol substituents. As in
other poly(amide) early transition metal structures,78,79
the various amide ligand substituents in 10 and 11 are
arranged so as to maximize 2pπ-3dπ bonding interactions.
Only one six-coordinate bis(phenolate)-diamine analo-
gue of 10 and 11 has been structurally authenticated,
namely, Ti(O2tBuNpy)(NMe2)2 (16).80 The overall geome-
tries of 10 and 11 are comparable with that of 16, with the
Ti-NMe2 distances in 10 (1.912(2), 1.916(2) A) being
slightly shorter than in the bis(phenolate) analogue
(1.927(3), 1.940(3) A).
Solid State Structures. The X-ray structures of all six
complexes 10-15 have been determined. We discuss first
the four titanium compounds 10-12 and 14. The mole-
cular structures are shown in Figures 4 and 5, and selected
distances and angles are listed in Tables 2 -5. All four
possess pseudo-octahedral titanium centers and approxi-
mately Cs molecular symmetry, consistent with the fast-
exchange limiting NMR spectra discussed above. In
general terms the metric parameters lie within the ex-
pected ranges to the types of linkages and functional
groups present.76 Unlike many of the previous titanium
structures with bi- and tridentate bis(sulfonamide)
ligands,60-62,66,67 none of these structures contain addi-
Comparisons can be made between Ti(Lpy)(OiPr)2 (12)
and Ti(LOMe)(OiPr)2 (14) and about 40 structurally
characterized, six-coordinate bis(phenolate)-supported
tional Ti O interaction to the tosyl substituents.
3 3 3
The average Ti-NTs distance in 10-12 and 14 (av.
2.096 A, range 2.069(5)-2.129(2) A) is slightly longer
than the values reported previously (av. 2.078 A, range
2.039-2.119 A). The average Ti-NTs distance of 2.108 A
in the bis(dimethylamide) complexes 10 and 11 is longer
than in the bis(isopropoxide) homologues (av. 2.086 A)
consistent with the better donor ability of NMe2
(78) Selby, J. D.; Manley, C. D.; Schwarz, A. D.; Clot, E.; Mountford, P.
Organometallics 2008, 27, 6479–6494.
(79) Ward, B. D.; Orde, G.; Clot, E.; Cowley, A. R.; Gade, L. H.;
Mountford, P. Organometallics 2004, 23, 4444–4461.
(80) Boyd, C. L.; Toupance, T.; Tyrrell, B. R.; Ward, B. D.; Wilson, C. R.;
Cowley, A. R.; Mountford, P. Organometallics 2005, 24, 309–330.

Article
Inorganic Chemistry, Vol. 48, No. 21, 2009 10447
Figure 5. (a) Displacement ellipsoid plot of Ti(Lpy)(OiPr)2 (12). (b) Displacement ellipsoid plot of Ti(LOMe)(OiPr)2 (14). Ellipsoids are drawn at the 20%
probablility level, and H atoms are omitted for clarity.
Table 2. Selected Bond Distances (A) and Angles (deg) for Ti(Lpy)(NMe2)2 (10)
Table 5. Selected Bond Distances (A) and Angles (deg) for Ti(LOMe)(OiPr)2 (14)
Ti(1)-N(1)
2.129(2)
2.099(2)
2.369(2)
2.282(2)
1.912(2)
131.72(11)
117.2(2)
110.9(2)
127.40(12)
116.4(2)
115.7(2)
Ti(1)-N(6)
1.916(2)
1.439(2)
1.447(2)
1.439(2)
1.445(2)
120.4(2)
131.0(2)
108.5(2)
122.2(2)
129.9(2)
107.6(2)
Ti(1)-O(1)
Ti(1)-O(2)
Ti(1)-O(3)
Ti(1)-N(1)
Ti(1)-N(2)
1.7920(18)
1.7534(18)
2.3271(18)
2.091(2)
Ti(1)-N(3)
S(1)-O(4)
S(1)-O(5)
S(2)-O(6)
S(2)-O(7)
2.0873(19)
1.436(2)
1.445(2)
1.4337(18)
1.4459(18)
Ti(1)-N(2)
S(1)-O(1)
Ti(1)-N(3)
S(1)-O(2)
Ti(1)-N(4)
S(2)-O(3)
Ti(1)-N(5)
S(2)-O(4)
2.277(2)
Ti(1)-N(1)-S(2)
Ti(1)-N(1)-C(1)
S(2)-N(1)-C(1)
Ti(1)-N(2)-S(1)
Ti(1)-N(2)-C(3)
S(1)-N(2)-C(3)
Ti(1)-N(5)-C(25)
Ti(1)-N(5)-C(26)
C(25)-N(5)-C(26)
Ti(1)-N(6)-C(27)
Ti(1)-N(6)-C(28)
C(27)-N(6)-C(28)
Ti(1)-O(1)-C(1)
Ti(1)-O(2)-C(4)
Ti(1)-O(3)-C(13)
Ti(1)-N(1)-S(1)
Ti(1)-N(1)-C(7)
146.1(3)
S(1)-N(1)-C(7)
Ti(1)-N(3)-S(2)
Ti(1)-N(3)-C(12)
S(2)-N(3)-C(12)
112.28(16)
127.23(11)
118.28(14)
114.45(15)
158.09(19)
120.41(16)
129.25(12)
118.42(16)
Table 3. Selected Bond Distances (A) and Angles (deg) for Ti(LOMe)(NMe2)2
(11)a
sulfonamide analogues with average values of 1.774 A
compared with a literature value of 1.804 A (range
1.749-1.852 A) in general and 1.813
1.806-1.832 A) for 17 and 18.
A (range
Ti(1)-N(1)
Ti(1)-N(2)
Ti(1)-N(3)
Ti(1)-N(4)
2.096(4)
2.201(7)
1.898(6)
1.981(7)
Ti(1)-O(3)
S(1)-O(1)
S(1)-O(2)
2.267(7)
1.439(4)
1.452(3)
The molecular structures of Zr(Lpy)(OiPr)2 (13) and
Zr(LOMe)(OiPr)2 (15) are shown in Figure 6, and selected
bond distances and angles are listed in Tables 6 and 7.
Crystals of 15 are isomorphous with those of 14, and the
molecular geometries are essentially identical. Five six-
coordinate bis(phenolate)-supported analogues of 15
have been structurally characterized, including the zirco-
nium congeners of 17 and 18.41,42 Their geometries are
again all comparable to that of 15 but the Zr-OiPr bond
lengths in the latter (1.910(2), 1.911(2) A) are shorter than
the bis(phenolate) examples (av. 1.943 A, range
1.910-1.967 A). This parallels the trends found in the
titanium systems.
Ti(1)-N(1)-S(1)
Ti(1)-N(1)-C(4)
S(1)-N(1)-C(4)
Ti(1)-N(3)-C(1)
C(1)-N(3)-C(1A)
129.6(2)
118.1(3)
112.2(3)
125.8(3)
108.4(6)
Ti(1)-N(4)-C(2)
Ti(1)-N(4)-C(3)
C(2)-N(4)-C(3)
Ti(1)-O(3)-C(8)
123.1(9)
136.1(9)
100.0(9)
120.1(10)
a Atoms carrying the suffix “A” are related to their counterparts by
the symmetry operator -x, y, -z þ 3/2.
Table 4. Selected Bond Distances (A) and Angles (deg) for Ti(Lpy)(OiPr)2 (12)
Ti(1)-O(1)
Ti(1)-O(2)
Ti(1)-N(1)
Ti(1)-N(2)
Ti(1)-N(3)
1.810(4)
1.741(4)
2.098(5)
2.264(5)
2.069(5)
Ti(1)-N(4)
S(1)-O(3)
S(1)-O(4)
S(2)-O(5)
S(2)-O(6)
2.278(6)
1.429(4)
1.447(4)
1.433(5)
1.444(5)
Only one monomeric zirconium sulfonamide com-
pound has been structurally characterized previously,
namely, the seven-coordinate Zr{1,2-C6H10(NTs)2}-
(NMe2)2(NHMe2) (Figure 2) which possesses two κ2(N,
O) bound NTs groups. As mentioned, this κ2(N,O) co-
ordination mode of NSO2R groups is very common for
Group 4 and other electron-deficient metals. As can be
seen from Figure 6, Zr(Lpy)(OiPr)2 (13) possesses one
κ2(N,O) bound NTs group giving an unsymmetrical
seven-coordinate metal center. This is in contrast to the
Cs, six-coordinate geometry of its congener, 12
(presumably because of the smaller atomic radius of
titanium), and also 15. However, the complicated solu-
tion phase NMR spectra mentioned above for 12, 14, and
Ti(1)-O(1)-C(1)
Ti(1)-O(2)-C(4)
Ti(1)-N(1)-S(1)
Ti(1)-N(1)-C(7)
139.2(4)
159.7(4)
125.0(3)
117.4(4)
S(1)-N(1)-C(7)
Ti(1)-N(3)-S(2)
Ti(1)-N(3)-C(16)
S(2)-N(3)-C(16)
117.3(4)
127.1(3)
116.3(4)
113.4(4)
bis(isopropoxide) complexes in general,76 including
Ti(O2RNpy)(OiPr)2 (17, R=Me or tBu) and Ti(O2RNMe )-
2
(OiPr)2 (18) specifically.41,42 The overall geometries are
comparable, as are the Ti-O-iPr angles (literature range
127-168°, av. 143°; for 12 and 14 range 139.2(4)-159.7-
(4)o, av. 150°). However, the Ti-OiPr distances are, as for
the Ti-NMe2 distances discussed above, shorter in the

10448 Inorganic Chemistry, Vol. 48, No. 21, 2009
Schwarz et al.
Figure 6. (a) Displacement ellipsoid plot of Zr(Lpy)(OiPr)2 (13). (b) Displacement ellipsoid plot of Zr(LOMe)(OiPr)2 (15). Ellipsoids are drawn at the 20%
probablility level, and H atoms are omitted for clarity.
Table 6. Selected Bond Distances (A) and Angles (deg) for Zr(Lpy)(OiPr)2 (13)
Table 8. Solution Polymerization of ε-CL by Ti(Lpy)(NMe2)2 (10), Ti(LOMe)-
(NMe2)2 (11), Ti(Lpy)(OiPr)2 (12), Zr(Lpy)(OiPr)2 (13), Ti(LOMe)(OiPr)2 (14), and
Zr(LOMe)(OiPr)2 (15)a
Zr(1)-O(1)
Zr(1)-O(2)
Zr(1)-O(3)
Zr(1)-N(1)
Zr(1)-N(2)
Zr(1)-N(3)
1.9644(16)
1.9260(16)
2.3498(16)
2.2332(19)
2.4933(19)
2.2779(19)
Zr(1)-N(4)
S(1)-O(3)
S(1)-O(4)
S(2)-O(5)
S(2)-O(6)
2.3880(19)
1.4881(17)
1.4370(18)
1.435(2)
yield time
(%)b (h)
Mn
(GPC)c
Mn
(calcd)d
Mw/
Mn
catalyst
1.4536(19)
Ti(Lpy)(NMe2)2 (10)
Ti(LOMe)(NMe2)2 (11)
Ti(Lpy)(OiPr)2 (12)
Ti(LOMe)(OiPr)2 (14)
Zr(Lpy)(OiPr)2 (13)
Zr(LOMe)(OiPr)2 (15)
97
95
93
87
91
93
12
22
9
1
1
12,990
5,710
1.91
14,260
5,720
6,390
5,180
7,770
5,710
5,710
5,710
5,710
5,710
1.60
1.80
1.39
1.19
1.18
Zr(1)-O(1)-C(1)
Zr(1)-O(2)-C(4)
Zr(1)-O(3)-S(1)
Zr(1)-N(1)-S(1)
Zr(1)-N(1)-C(7)
145.76(16)
148.07(15)
99.27(8)
102.18(10)
129.31(15)
S(1)-N(1)-C(7)
Zr(1)-N(3)-S(2)
Zr(1)-N(3)-C(16)
S(2)-N(3)-C(16)
128.20(17)
132.48(11)
113.47(14)
114.03(16)
1
a Conditions: [ε-CL]/[catalyst] = 100:1, 6.8 mL of toluene at 100 °C.
See Experimental Section for other details. b Isolated yield at 100%
NMR conversion. c Molecular weights (g mol-1) determined from GPC
using the appropriate Mark-Houwink corrections. d Expected Mn (g
mol-1) for 2 chains growing per metal center at 100% conversion. For
Table 7. Selected Bond Distances (A) and Angles (deg) for Zr(LOMe)(OiPr)2 (15)
Zr(1)-O(1)
Zr(1)-O(2)
Zr(1)-O(3)
Zr(1)-N(1)
Zr(1)-N(2)
1.910(2)
1.911(2)
2.393(2)
2.227(3)
2.434(3)
Zr(1)-N(3)
S(1)-O(4)
S(1)-O(5)
S(2)-O(6)
S(2)-O(7)
2.216(2)
1.440(3)
1.441(2)
1.439(2)
1.444(2)
one chain per metal center the calculated value is 11,410 g mol-1
.
negligible conversions, presumably because of THF com-
petition for coordination to the metal center. Subsequent
studies were performed in toluene at 100 °C, and under
these conditions all the complexes were found to be active.
The progress of each reaction was monitored by regular
sampling, and the results summarized in Table 8 corre-
spond to when the polymerizations eventually reached
100% conversion. The molecular weights and PDIs (Mw/
Mn) were determined by gel permeation chromotography
(GPC) using the appropriate Mark-Houwink corrections,
Zr(1)-O(1)-C(1)
Zr(1)-O(2)-C(4)
Zr(1)-O(3)-C(13)
Zr(1)-N(1)-S(1)
Zr(1)-N(1)-C(7)
148.4(3)
155.3(2)
120.3(2)
123.56(15)
121.33(19)
S(1)-N(1)-C(7)
Zr(1)-N(3)-S(2)
Zr(1)-N(3)-C(12)
S(2)-N(3)-C(12)
115.1(2)
122.23(14)
121.06(19)
116.7(2)
15 imply that several more coordination geometries may
be accessible in solution. The Zr-OiPr and Zr-N dis-
tances in 13 are all longer than the corresponding ones in
15 reflecting the higher coordination number of the
former. The S(1)-O(3) distance for the bridging sulfo-
namide oxygen is 0.051(3) A longer than the terminal
S(1)-O(4) bond as expected.
Overall the geometries of 10-15 parallel those of the
well-established bis(phenolate) complexes but with slightly
shorter Ti-NMe2 and M-OiPr distances and the potential
in both the solid state and solution for additional stabiliza-
81-83
and the yield refers to the amount of poly(ε-CL)
isolated. The Mn(calcd) values are those expected for two
polymer chains growing per metal center (i.e., one chain per
Ti-NMe2 or M-OiPr bond in the starting complex) at
100% conversion of monomer.
The bis(dimethylamide) catalysts Ti(LR)(NMe2)2 (10
and 11) were the slowest of the six evaluated. The GPC
data are consistent with only one poly(ε-CL) chain for-
ming per metal (Mn(calcd)=11,420 g mol-1) on average.
This is consistent with the rate of initiation by the expected
coordination-insertion mechanism32 (insertion of ε-CL
tion of the metal centers via M
OTs interactions.
3 3 3
Polymerization Studies: ROP of ε-CL. A principal aim
of this work was to evaluate the potential of sulfonamide-
supported Group 4 complexes for the catalytic ROP of
ε-CL and rac-LA. An initial study using the six compounds
10-15 was undertaken using ε-CL because of the relative
ease of its polymerization due to the favorable release of
7-membered ring strain. Initial studies performed in tetra-
hydrofuran (THF) gave extremely long reaction times and
(81) Alfred, R.; Howard, L. W. H. J. Polym. Sci., Part A: Polym. Chem.
1972, 10, 217–235.
ꢀ ^
(82) Barakat, I.; Ph D.; Jerome, R.; Ph T. J. Polym. Sci., Part A: Polym.
Chem. 1993, 31, 505–514.
(83) John, R. D.; Jay, J.; Daniel, M. K.; Sukhendu, B. H.; Bradford, R. L.;
Matthew, H. H. J. Polym. Sci., Part B: Polym. Phys. 2005, 43, 3100–3111.

Article
Inorganic Chemistry, Vol. 48, No. 21, 2009 10449
Table 9. First Order Propagation Rate Constant (kp) for ε-CL Polymerization by
Ti(Lpy)(OiPr)2 (12), Zr(Lpy)(OiPr)2 (13), Ti(LOMe)(OiPr)2 (14), and Zr(LOMe)-
(OiPr)2 (15)a
catalyst
kp (min-1
)
Ti(Lpy)(OiPr)2 (12)
Ti(LOMe)(OiPr)2 (14)
Zr(Lpy)(OiPr)2 (13)
Zr(LOMe)(OiPr)2 (15)
0.0075(7)
0.065(3)
0.108(5)
0.121(4)
a Conditions: [ε-CL0]/[M(LR)(OiPr)2] = 100:1, 6.8 mL of toluene,
100 °C.
Figure 7. First order plot for ε-CL consumption using Zr(LOMe)(OiPr)2
(15). Conditions: [ε-CL0]/[15] = 100:1, 6.8 mL of toluene, 100 °C, 0.1 mL
aliquots taken at the given intervals. See Experimental Section for other
details. Linear fit (r2 = 0.995) shown is for the first order region after the
inductionperiod. See the SupportingInformationfor correspondingplots
for 12, 13, and 14.
Figure 9. Plot of % conversion vs time for the polymerization of two
consecutive batches of ε-CL using Zr(LOMe)(OiPr)2 (15). Conditions
[CL0]/[15] = 100:1 followed by a further 100 equiv at t = 400 min,
0.75 mL of C6D6, 70 °C.
Representative plots are shown in Figures 7 and 8 for
Zr(LOMe)(OiPr)2 (15). Analogous plots for 12-14 are
shown in the Supporting Information. First order propa-
gation rate constants (kp) obtained from the linear part of
the log plots are given in Table 9.
Figure 8. Plots of Mn and PDI (determined by GPC) vs conversion for
the polymerization of ε-CL using Zr(LOMe)(OiPr)2 (15). Conditions:
[ε-CL0]/[15] = 100:1, 6.8 mL of toluene, 100 °C, 0.1 mL aliquots taken
at the given intervals. Hollow diamonds correspond to Mn and hollow
circles to PDI.
Catalysts 13-15 show a relatively short induction
period of 5-10 min followed by a polymerization process
that is first order with respect to ε-CL concentration
(Figure 7). Similar induction periods have been observed
for main group and transition metal isopropoxide cata-
lysts.20,42,84 The induction period for Ti(Lpy)(OiPr)2 (12,
see the Supporting Information) was substantially longer
(ca. 60-70 min) than the other three. The kp values
(Table 9) show two main features. First, as found for
the corresponding bis(phenolate) systems,41,42 the zirco-
nium catalysts are faster than the titanium ones for a
given LR supporting ligand. Second, there is a pendant
arm effect for both pairs of catalyst with the kp values for
Lpy-supported systems being less than for their LOMe
analogues (considerably so in the case of 12 and 14). We
interpret both of these effects in terms of easier access to
the metal center since Zr is larger than Ti and OMe is a
more labile donor than pyridyl.
Catalysts 13, 14, and 15 gave reasonably linear plots of
Mn versus % conversion (Figure 8 and the Supporting
Information) with narrow PDIs (1.10-1.20 for 13 and 15,
somewhat broader for the less well-behaved 14) which
remained effectively constant throughout the process.
The gradients of the Mn versus % conversion plots were
47(2), 64(4), and 67(3) g mol-1 (% conversion)-1 (av. 59 g
mol-1 (% conversion)-1) which are close to that expected
(57 g mol-1 (% conversion)-1) for two poly(ε-CL) chains
growing per metal center. All of these data are consistent
into Ti-NMe2) being much slower than propagation
(insertion of subsequent ε-CLs into the growing Ti-
{O(CH2)5C(O)}nNMe2 chain). Analogous effects have been
recorded elsewhere.50 Although the observed and calculated
Mn values for the poly(ε-CL) formed with 10 and 11 are in
fairly good agreement for a living-type process, the broad
PDIs of 1.91 and 1.60 show that there is poor control in
terms of the distribution of molecular weights. Our further
efforts therefore focused on the bis(isopropoxide) systems.
Changing from Ti(LR)(NMe2)2 (10 and 11) to Ti(LR)-
(OiPr)2 (12 and 14) gave a clear switch from about one to
two poly(ε-CL) chains per metal center and also
(especially for 14) a significant increase in activity. The
zirconium analogues 13 and 15 were, according to the
primary screen in Table 8, at least as productive as 14, also
forming two chains per metal center. In addition, the PDI
values for these two catalysts indicated a better controlled
polymerization process than for any of the titanium
1
systems. H NMR and MALDI-ToF-MS analysis (see
the Supporting Information for examples) of all four
poly(ε-CL)s showed one OiPr end group per chain, con-
sistent with a coordination-insertion mechanism.32
Further experiments were carried out with 12-15 to
evaluate the kinetic behavior and first order rates of
propagation, and also how M n increases with conversion.
(84) Duda, A.; Penczek, S. Macromolecules 1995, 28, 5981–5992.

10450 Inorganic Chemistry, Vol. 48, No. 21, 2009
Schwarz et al.
with these species acting as living catalysts for ROP
of ε-CL.
To make a proper comparison with previously reported
bis(phenolate)amine systems, we also evaluated David-
son et al.’s57 ROP catalyst Zr(O2MeNpy)(OiPr)2 (19) under
the same conditions as 12-15. This had a slightly shorter
induction period (5 min) and a kp of 0.226(8) s-1. The kp
for compound 19 is therefore twice that of the most
comparable bis(sulfonamide) catalyst 13 (kp = 0.108(5)
s
-1). However, the corresponding sulfonamide demon-
strated a more controlled polymerization process with a
Mn of 5,180 g mol-1 and a PDI of 1.19 compared to 19
which yielded poly(ε-CL) with a Mn of 8,000 g mol-1 and
a PDI of 1.55, where the calculated value of Mn for 2
Figure 10. First order plot for rac-LA consumption using Zr(LOMe)-
(OiPr)2 (15). Conditions [rac-LA0]/[15] = 100:1, 6 mL of toluene, 70 °C,
0.1 mL aliquots taken at the given intervals. See Experimental Section for
otherdetails. Linearfit(r2 =0.996)shown is forthe firstorderregion after
the induction period.
chains per metal center is 5,710 g mol-1
.
As a final probe of the living characteristics of the
most active catalyst, namely, 15, polymerization re-
sumption experiments were undertaken in which 100
equiv of ε-CL were polymerized on the NMR tube scale
at 70 °C in C6D6. Once full conversion had been ob-
served, a further 100 equiv were added, and the reaction
once again was monitored until completion (Figure 9).
Consistent with Figure 7, the data in Figure 9 indicate a
short induction period before becoming first order in
monomer concentration (see the Supporting Informa-
tion for the corresponding semilogarithmic plots). Inter-
estingly, the second 100 equiv of monomer show
minimal induction period, presumably because the ac-
tive catalyst is fully formed after the initial polymeriza-
tion and is still “living”. The kp values for both parts of
Figure 9 (i.e., the first and second portions of ε-CL) are
identical at 0.009(1) min-1. GPC analysis of the poly-
(ε-CL) showed a narrow PDI (1.19) and an Mn of
9,980 g mol-1 which is in reasonable agreement with
the Mn(calcd) value of 11,410 g mol-1 for two chains per
metal center.
Polymerization Studies: ROP of rac-LA. The studies of
the ROP of ε-CL showed Zr(Lpy)(OiPr)2 (13) and Zr-
(LOMe)(OiPr)2 (15) to be the best catalysts in terms of
activity and polymerization control. Our studies were
next extended to the more challenging monomer, rac-
LA. Preliminary experiments showed 15 to be signifi-
cantly more active than 13, but with otherwise similar
ROP features (control of Mn, PDI). We therefore fo-
cused on 15 for detailed studies. Solution polymeriza-
tions were performed in toluene at 70 °C until about
95% completion. As shown in Figure 10 the polymeri-
zation follows first order consumption of rac-LA
(kp = 0.0076(2) min-1) and there is again a noticeable
induction period.20,42,84
Figure 11. Plots of Mn and PDI (determined by GPC) vs conversion for
the solution polymerization of rac-LA using Zr(LOMe)(OiPr)2 (15). Con-
ditions: [rac-LA0]/[15] = 100:1, 6.0 mL of toluene, 70 °C, 0.1 mL aliquots
taken at the given intervals. Hollow diamonds correspond to Mn and
hollow circles to PDI.
Figure 11 shows that Mn increases linearly with con-
version in a living fashion. The final experimental Mn
(94% conversion) of 8,290 g mol-1 is in good agreement
with the expected value of 6,740 g mol-1 if two rac-LA
chains were growing per metal center. The gradient of the
plot is 88(1) g mol-1 (% conversion)-1 which compares
favorably with the expected value (72 g mol-1 (% con-
version)-1). Figure 11 also shows that the PDIs remain
very narrow and effectively constant between 1.12 and
1.14 throughout the process, consistent with a single site
catalyst. The 1H NMR and MALDI-ToF-MS spectra of
the poly(rac-LA) show the expected single OiPr end group
per chain, consistent with a coordination-insertion me-
chanism. Unfortunately, the selectively homonuclear de-
coupled 1H NMR spectrum showed that the polymer was
effectively atactic (in accord with the behavior of the
corresponding bis(phenolate)amine-supported catalysts)
and so under these conditions the bis(sulfonamide) sup-
porting ligand is not able to significantly influence the
enchainment preferences of L-LA and D-LA (chain end
control). The separation between the m/z envelopes in the
MALDI-TOF-MS (see the Supporting Information) was
72 g mol-1 which is half the molecular weight of a single
lactidyl unit and therefore indicative of extensive inter-
molecular transesterification during the polymerization
process as is very often observed with metal-based cata-
lysts.

Article
Inorganic Chemistry, Vol. 48, No. 21, 2009 10451
for their synthesis certainly testify to the equilibrium nature
of the reactions. The amide complexes 10 and 11 were found
to be poor catalysts for the ROP of ε-CL, and long reaction
times and poor control were observed. This is attributed to
the greater dissimilarity between the initiating group
Ti-NMe2 and the subsequent growing chain Ti-{O-
(CH2)5C(O)}nNMe2, as well as to the smaller radius of Ti
compared with Zr. With respect to the Group 4 isopropoxide
complexes, the ROP results for ε-CL were in agreement with
literature precedent in that the zirconium homologues were
more active than their titanium counterparts. Polymerization
rates were higher for the catalysts bearing an OMe donor (14
and 15) compared to a pyridyl one. The zirconium catalyst 15
was found to be an active and well-controlled catalyst for the
living ROP of rac-LA both in solution and in the melt. All
poly(rac-LA)s formed were predominantly atactic. Further
work in our laboratory is underway to assess different
sulfonamide substituents and ligand backbone motifs to
increase catalyst activity and control.
Figure 12. Plots of Mn and PDI (determined by GPC) vs conversion
for the melt polymerization of various equivalents of rac-LA using
Zr(LOMe)(OiPr)2 (15). Conditions: [rac-LA0]/[15] = various values bet-
ween 50:1 and 300:1, 130 °C, 30 min. See Experimental Section for other
details. Hollow diamonds correspond to Mn and hollow circles to PDI.
Polymerization experiments were also undertaken un-
der industrially relevant melt conditions to evaluate
catalyst 15 (Figure 12).85,86 Excellent conversions
(ca. 90%) of between 50 and 300 starting equivalents of
rac-LA in 30 min at 130 °C were obtained giving atactic,
isopropoxy-terminated polymers with Mn values up to
42,430 g mol-1 (PDI=1.49) for the experiment starting
with 300 equiv of rac-LA. This value compares fairly well
with an expected Mn of 37,690 g mol-1 for one chain per
metal. The gradient of the Mn versus equivalents of rac-
LA polymerized plot (Figure 12) is 149(16) g mol-1
equiv-1 which is the same within error as the expected
value of 144 for one chain per metal center and consistent
with a living catalyst. It is not clear why only one chain
grows per metal center in the melt compared to two per
metal in solution. The polymers had broader PDIs than in
the solution experiments (carried out at lower
temperature) as expected. Again the poly(rac-LA) was
predominantly atactic. Nonetheless, the activity of 15
under these conditions is superior to those of the afore-
mentioned bis(phenolate) systems which gave up to 75%
conversion over somewhat longer reaction times (2 h),57
and is comparable to the tris(phenolate) systems of the
type 4 in Figure 1 (50 or 95% conversion after 0.5 h (M=
Ti or Hf); 78% conversion after 0.1 h (M=Zr) for [rac-
LA]:[4]=300).42,54
Experimental Section
General Methods and Instrumentation. All manipulations
were carried out using standard Schlenk line or drybox techni-
ques 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. Toluene
was refluxed over sodium and distilled. Deuterated solvents
were dried over sodium (C6H6) 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
Varian Mercury-VX 300 and Varian Unity Plus 500 spectro-
meters 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 confirmed using two-dimen-
sional 1H-1H and 13C-1H NMR correlation experiments.
Chemical shifts are quoted in δ (ppm) and coupling constants
in hertz. IR spectra were recorded on a Nicolet Magna 560 ESP
FTIR spectrometer. Samples were prepared 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.
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
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 detec-
tor. THF (HPLC grade) was used as an eluent at 30 °C with a
rate of 1 mL min-1. Linear polystyrenes were used as primary
calibration standards, and Mark-Houwink corrections for
poly(ε-CL) or poly(rac-LA) in THF were applied for the
experimental samples.81-83
Conclusions
In this contribution we have reported the first transition
metal sulfonamide-supported catalysts for the ROP of ε-CL
and rac-LA. The productivities of these new complexes are
comparable to those of the well-established and thoroughly
explored bis(phenoxide) and related Group 4 analogues. The
new bis(amide) complexes Ti(Lpy)(NMe2)2 (10) or Ti(LOMe)-
(NMe2)2 (11) were easily prepared under mild conditions
because of the high basicity of the NMe2 ligand, whereas the
bis(isopropoxide) analogues M(Lpy)(OiPr)2 and M(LOMe)-
(OiPr)2 (12-15) required more forcing conditions when
starting from the homoleptic precursors. Indeed, it is some-
what surprising that the sulfonamides H2LR (8, 9) were able
to displace iPrOH at all, and the reaction conditions required
ꢀ
(85) Vink, E. T. H.; Rabago, K. R.; Glassner, D. A.; Gruber, P. R. Polym.
Degrad. Stab. 2003, 80, 403–419.
(86) Drumright, R. E.; Gruber, P. R.; Henton, D. E. Adv. Mater. 2000, 12,
1841–1846.

10452 Inorganic Chemistry, Vol. 48, No. 21, 2009
Schwarz et al.
Starting Materials. Ti(NMe2)4,87,88 Ti(NMe2)2(OiPr)2,89,90
H2Lpy (8),74 and H2LOMe (9)75 were synthesized according to
published procedures. ε-CL was dried over freshly ground CaH2
and distilled before use. rac-LA was recrystallized twice from
toluene and then sublimed twice prior to use. Other reagents
were purchased from Sigma-Aldrich and used without further
purification.
OCHMe2 cis to py), 1.37 (6H, d, 3J=6.1 Hz, OCHMe2 trans to
py) ppm. 13C-{1H} NMR (CD2Cl2, 75.4 MHz): δ 158.8 (6-
NC5H4), 152.2 (2-NC5H4), 143.4 (1-C6H4Me), 143.2 (4-
C6H4Me), 140 (3-NC5H4), 131.4 (3-C6H4Me), 128.1 (2-
C6H4Me), 125.6 (4-NC5H4), 121.6 (5-NC5H4), 85.4 (OCHMe2
cis to py), 81.7 (OCHMe2 trans to py), 62.9 (pyCH2N), 61.8
(TsNCH2CH2N), 50.9 (TsNCH2CH2N), 28.6 (OCHMe2 cis to
py), 28.3 (OCHMe2 trans to py), 23.4 (C6H4Me) ppm. IR: 3435
(w), 1607 (s), 1290 (m), 1280 (m), 1141 (s), 1088 (s), 1018 (s), 969
(m), 942 (m), 920 (m), 854.5 (w), 832 (m), 774 (w), 665 (m), 600
Ti(Lpy)(NMe2)2 (10). A slurry of H2Lpy (0.25 g, 0.50 mmol) in
benzene (30 mL) was added to a solution of Ti(NMe2)4
(0.12 mL, 0.50 mmol) in benzene (10 mL). The mixture was
stirred for 19 h, resulting in a dark red solution with brown
percipitate. The solid was filtered off and washed with pentane
(3 ꢀ 30 mL). Recrystallization from a saturated benzene solu-
tion yielded 10 as a brick-red solid that was washed with pentane
(3 ꢀ 20 mL) and dried in vacuo. Yield: 0.17 g (55%). 1H NMR
(CD2Cl2, 299.9 MHz, 303 K): δ 8.91 (1H, m, 2-NC5H4), 8.31
(1H, m, 4-NC5H4), 7.78 (1H, app. t, 3J=6.9 Hz, 3-NC5H4), 7.52
(m), 554 (m), 508 (m) cm-1
. Anal. found (calcd. for
C30H42N4O6S2Ti); C, 54.05 (54.05); H, 6.45 (6.35); N, 8.28
(8.40) %.
Alternative NMR Tube Scale Synthesis of Ti(Lpy)(OiPr)2 (12).
To a solution of Ti(NMe2)2(OiPr)2 (6.1 mg, 23.8 μmol) in
CD2Cl2 (0.2 mL) was added a solution of H2Lpy (12 mg, 23.8
μmol) in CD2Cl2 (0.2 mL). A color change of the initially light
3
1
(1H, d, J=4.3 Hz, 2-C6H4Me), 7.20 (1H, m, 5-NC5H4), 7.12
(1H, d, J=4.5 Hz, 3-C6H4Me), 3.79 (6H, s, NMe2 cis to py),
brown to light yellow was observed. After 1 h analysis by H
NMR indicated that 12 had been formed quantitatively.
Zr(Lpy)(OiPr)2 (13). A slurry of H2Lpy (1.00 g, 2.00 mmol) in
3
3.59 (4H, br. m, overlapping pyCH2 and TsNCH2), 3.44 (6H, br.
s, NMe2 trans to py), 3.21 (2H, br. m, TsNCH2CH2), 2.87 (4H,
br. m, TsNCH2CH2), 2.37 (6H, s, C6H4Me) ppm. A satisfactory
13C NMR spectrum could not be obtained because of the
fluxional nature of the compound. IR: 3464 (w), 1255 (w),
1143 (m), 1088 (m), 947 (m), 665 (m), 511 (w) cm-1. Anal. found
(calcd. for C28H40N6O4S2Ti): C, 52.85 (52.82); H, 6.33 (6.26); N,
13.15 (13.20) %.
toluene (50 mL) was added to a solution of Zr(OiPr)4 HOiPr
3
(3.00 g, 7.80 mmol) in toluene (20 mL). The mixture was heated
at 100 °C for 16 h, resulting in an off-white slurry. The solid was
filtered off and washed with pentane (3 ꢀ 30 mL). Recrystalliza-
tion from a saturated benzene solution layered with hexanes
yielded 13 as a white solid that was washed with pentane (3 ꢀ 20
mL) and dried in vacuo. Yield: 0.60 g (42%). 1H NMR (C6D6,
299.9 MHz, 343 K): δ 9.47 (1H, br. m, 2-NC5H4), 8.25 (4H, br. d,
3J=6.0 Hz, 2-C6H4Me), 6.95 (5H, br. d, 3J=6.0 Hz, overlapping
3-C6H4Me and 4-NC5H4), 6.68 (1H, br. m, 3-NC5H4), 6.42 (1H,
Ti(LOMe)(NMe2)2 (11). A slurry of H2LOMe (0.16 g, 0.34 mmol)
in benzene (60 mL) was added to a solution of Ti(NMe2)4
(0.6 mL, 2.54 mmol) in benzene (20 mL). The mixture was
heated at 70 °C for 16 h, resulting in a dark red solution.
Removal of the volatiles under reduced pressure yielded a dark
red solid that was recrystallized from a concentrated benzene
solution to yield 11 as a red solid which was washed with pentane
(3 ꢀ 20 mL) and dried in vacuo. Yield: 0.11 g (51%). 1H NMR
(CD2Cl2, 299.9 MHz): δ 7.72 (4H, d, 3J=6.1 Hz, 2-C6H4Me),
7.29 (4H, d, 3J=6.1 Hz, 3-C6H4Me), 3.54 (6H, s, NMe2 cis to
OMe), 3.43-3.34 (9H, m, overlapping OMe, OCH2 and
TsNCH2), 3.20 (6H, s, NMe2 trans to OMe), 2.82 (6H, m,
overlapping OCH2CH2 and TsNCH2CH2), 2.40 (6H, s,
C6H4Me). 13C-{1H} NMR (CD2Cl2, 75.4 MHz): δ 141.8 (1-
C6H4Me), 140.4 (4-C6H4Me), 130.4 (3-C6H4Me), 127.9 (2-
C6H4Me), 69.7 (TsNCH2), 61.3 (OCH2), 55.7 (TsNCH2CH2),
51.4 (OCH2CH2), 49.6 (cis to OMe NMe2), 49.5 (TsNCH2), 49.3
(NMe2 trans to OMe), 21.6 (C6H4Me). IR: 3446 (w) 1302 (m),
1295 (w), 1284 (m), 1139 (m), 1020 (s), 943 (s), 864 (m), 666 (m),
554 (w) cm-1. Anal. found (calcd. for C25H41N5O5S2Ti); C,
49.60 (49.74); H, 6.94 (6.85); N, 11.48 (11.60) %.
Ti(Lpy)(OiPr)2 (12). A slurry of H2Lpy (0.75 g, 1.50 mmol) in
toluene (50 mL) was added to a solution of Ti(OiPr)4 (2.2 mL,
7.5 mmol) in toluene (20 mL). The mixture was heated at 100 °C
for 16 h, resulting in an off-white slurry. The solid was filtered
off and washed with pentane (3 ꢀ 30 mL). Recrystallization
from a saturated dichloromethane solution layered with pen-
tane yielded 12 as a beige solid that was washed with hexanes
(3 ꢀ 20 mL) and dried in vacuo. Yield: 0.62 g (62%). 1H NMR
(CD2Cl2, 299.9 MHz): δ 8.76 (1H, dd, 3J=4.7 Hz, 4J=6.0 Hz, 2-
NC5H4), 7.66 (1H, dt, 3J=4.7 Hz, 3J=9.0 Hz, 4-NC5H4), 7.46
(4H, d, 3J = 7.9 Hz, 2-C6H4Me), 7.12 (6H, d, 3J = 7.9 Hz,
overlapping 3-C6H4Me, 3- and 5-NC5H4), 5.32 (1H, sept., 3J=
6.1 Hz, OCHMe2 cis to py), 5.16 (1H, sept., 3J = 6.1 Hz,
OCHMe2 trans to py), 3.94 (2H, s, pyCH2N), 3.40 (4H, m,
TsNCH2CH2N), 3.10 (2H, m, TsNCH2CH2N), 2.88 (2H, m,
TsNCH2CH2N), 2.35 (6H, s, C6H4Me), 1.51 (6H, d, 3J=6.1 Hz,
3
3
br. d, J=6.1 Hz, 5-NC5H4), 5.16 (1H, br. sept, J=6.0 Hz,
OCHMe2 cis to py), 4.62 (1H, br. sept, J=6.1 Hz, OCHMe2
3
trans to py), 3.62 (2H, br. s, pyCH2), 3.17, (4H, br. m,
TsNCH2CH2), 2.54 (4H, TsNCH2CH2), 1.97 (6H, s, C6H4Me),
1.58 (6H, br. d, 3J=6.1 Hz, CHMe2 cis to py), 1.20 (6H, br. d,
3J = 6.1 Hz, CHMe2 trans to py). A satisfactory 13C NMR
spectrum could not be obtained because of the fluxional nature
of the compound. IR: 3431 (w), 1605 (w), 1164 (m), 1016 (m),
961 (w), 815 (m), 723 (w), 666 (m), 557 (w) cm-1. Anal. found
(calcd. for C30H42N4O6S2Zr); C, 50.85 (50.75); H, 5.92 (5.96); N,
7.89 (7.89) %.
Ti(LOMe)(OiPr)2 (14). A mixture of H2LOMe (0.15 g, 0.32
mmol) and Ti(OiPr)4 (2.0 mL, 6.76 mmol) was heated and stirred
at 130 °C under dynamic vacuum (70 mbar) for 4 h. The mixture
was cooled to RT resulting in a yellow solid which was recrys-
tallized from saturated dichloromethane solution layered with
pentane to yield 14 as a yellow solid that was washed with
1
pentane (3 ꢀ 20 mL) dried in vacuo. Yield: 0.10 g (47%). H
NMR (CD2Cl2, 299.9 MHz): δ 7.74 (4H, d, 3J = 9.0 Hz, 2-
C6H4Me), 7.25 (4H, d, 3J=9.0 Hz, 3-C6H4Me), 5.16 (1H, sept.,
3J=6.5 Hz, OCHMe2 cis to OMe), 4.93 (1H, sept., 2J=6.5 Hz,
OCHMe2 trans to OMe), 3.91 (3H, s, OMe), 3.80 (2H, t, 3J=6.5
Hz, MeOCH2), 3.42-3.12 (6H, m, overlapping TsNCH2 and
TsNCH2CH2), 2.74 (4H, m, overlapping MeOCH2CH2 and
TsNCH2CH2), 2.37 (6H, s, C6H4Me), 1.41 (4H, d, 3J=6.5 Hz,
OCHMe2 cis to OMe), 1.14 (4H, d, 3J=6.5 Hz, OCHMe2 trans
to OMe) ppm. 13C-{1H} NMR (CD2Cl2, 75.4 MHz) δ 141.6 (1-
C6H4Me), 141.5 (4-C6H4Me), 129.4 (3-C6H4Me), 127.3 (2-
C6H4Me), 84.5 (OCHMe2 cis to OMe), 81.5 (OCHMe2 trans
to OMe), 71.6 (MeOCH2), 63.9 (OMe), 58.1 (TsNCH2), 54.6
(MeOCH2CH2), 48.7 (TsNCH2CH2), 26.1 (OCHMe2 trans to
OMe), 25.9 (OCHMe2 cis to OMe), 21.6 (C6H4Me) ppm. IR:
3428 (w), 1297 (m), 1284 (s), 1145 (s), 1090 (s), 959 (m), 855 (m),
829 (s), 758 (w), 602 (m), 506 (w) cm-1. Anal. found (calcd.
for C27H43N3O7S2Ti); C, 51.08 (51.18); H, 6.88 (6.84); N, 6.61
(6.63) %.
(87) Bradley, D. C.; Thomas, I. M. J. Chem. Soc. 1960, 3857.
(88) Diamond, G. M.; Jordan, R. F.; Petersen, J. L. Organometallics 1996,
15, 4030–4037.
(89) Benzing, E.; Kornicker, W. Chem. Ber. 1961, 2263–2267.
(90) Kempe, R.; Arndt, P. Inorg. Chem. 1996, 35, 2644–2649.
Alternative Synthesis of Ti(LOMe)(OiPr)2 (14). A solution of
H2LOMe (0.50 g, 1.1 mmol) in dichloromethane (30 mL) was
added to a solution of Ti(NMe2)2(OiPr)2 (0.30 g, 1.2 mmol) in

Article
Inorganic Chemistry, Vol. 48, No. 21, 2009 10453
Table 10. X-ray Data Collection and Processing Parameters for H2LOMe (9), Ti(Lpy)(NMe2)2 (10), Ti(LOMe)(NMe2)2 2(C6H6) (11 2(C6H6)), Ti(Lpy)(OiPr)2 (12),
3
3
Ti(LOMe)(OiPr)2 (14), Zr(Lpy)(OiPr)2 (13), and Zr(LOMe)(OiPr)2 (15)
9
10
11 2(C6H6)
3
12
empirical formula
fw
temp/K
wavelength/A
space group
a/A
b/A
c/A
R/deg
β/deg
γ/deg
V/A3
C21H31N3O5S2
469.63
150
0.71073
P 212121
7.34540(10)
13.02980(10)
24.3794(3)
90
C28H40N6O4S2Ti
636.70
150
0.71073
P21/c
9.7433(3)
18.4302(5)
17.1845(5)
90
90.163(1)
90
C25H41N5O5S2Ti 2(C6H6)
3
C30H42N4O6S2Ti
666.70
150
0.71073
P21/c
8.9177(18)
9.6354(19)
36.811(7)
90
90.00(3)
90
759.89
150
0.71073
C2/c
13.9610(5)
12.7787(5)
21.6251(10)
90
93.0481(12)
90
3852.5(3)
4
1.310
90
90
2333.33(5)
4
1.337
3085.8(2)
4
1.370
3163.0(11)
4
1.400
Z
d (calcd)/Mg m-3
3
abs coeff/mm-1
R indices:a
R1 =
0.265
0.456
0.378
0.451
0.0298b
0.0341b
0.0380b
0.0379b
0.0672b
0.0670b
0.0788c
0.2026
15
Rw =
wR2 =
14
13
empirical formula
fw
temp/K
wavelength/A
space group
a/A
b/A
c/A
R/deg
β/deg
γ/deg
V/A3
C27H43N3O7S2Ti
633.66
150
0.71073
P21/c
9.9927(1)
9.6963(1)
31.4855(4)
90
92.733(1)
90
C30H42N4O6S2Zr
710.04
150
0.71073
P1
9.2206(2)
9.6331(2)
18.7269(5)
85.4348(14)
78.1548(15)
84.6582(16)
1617.76(7)
2
C27H43N3O7S2Zr
677.01
150
0.71073
P21/c
10.01950(10)
9.89890(10)
31.5596(4)
90
92.7258(6)
90
3047.23(6)
4
1.381
3126.60(6)
4
1.438
Z
d (calcd)/Mg m-3
1.458
0.517
3
abs coeff/mm-1
R indices:a
R1 =
0.466
0.532
0.0400c
0.0980d
0.0326b
0.0370b
0.0376b
0.0355b
Rw =
wR2 =
√
√
{
P
P
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|; Rw =
I > 2σ(I). d For all data.
{
w (|Fo| - |Fc|)2/ w|Fo|2}; wR2 =
w(Fo2 - Fc2)2/ w(Fo2)2}. b For data with I > 3σ(I). c For data with
dichloromethane (30 mL). The mixture was stirred for 2 h,
resulting in a yellow solution. Removal of the volatiles under
reduced pressure afforded a yellow solid that was recrystallized
from a concentrated dichloromethane solution layered with
pentane to give 14 as a yellow solid that was washed with
pentane (3 ꢀ 20 mL) and dried in vacuo. Yield: 0.52 g (78%).
Zr(LOMe)(OiPr)2 (15). A mixture of H2LOMe (0.11 g, 0.23
C
27H43N3O7S2Zr); C, 47.87 (47.90); H, 6.31 (6.40); N, 6.17
(6.21) %.
Crystal Structure Determinations of H2LOMe (9), Ti(Lpy)(NMe2)2
(10), Ti(LOMe)(NMe2)2 (11), Ti(Lpy)(OiPr)2 (12), Zr(Lpy)(OiPr)2
(13), Ti(LOMe)(OiPr)2 (14), and Zr(LOMe)(OiPr)2 (15). Crystal data
collection and processing parameters are given in Table 10.
Crystals were mounted on glass fibers using perfluoropolyether
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 appro-
priate, absorption and decay corrections were applied to the
data and equivalent reflections merged.91 The structures were
solved with SIR9292 or SHELXS-9793 and further refinements
and all other crystallographic calculations were performed using
either the CRYSTALS program suite94 or SHELXS-97.95 Other
mmol) and Zr(OiPr)4 HOiPr (0.50 g, 1.29 mmol) was heated
3
with stirring at 125 °C under dynamic vacuum (75 mbar) for
5 h. The mixture was cooled to RT resulting in a yellow solid
which was crystallized from saturated dichloromethane solu-
tion layered with pentane to yield 15 as a pale yellow solid that
was washed with pentane (3 ꢀ 20 mL) and dried in vacuo.
Yield: 0.07 g (41%). 1H NMR (CD2Cl2, 499.9 MHz, 273 K): δ
7.82 (4H, br. d, 3J=7.0 Hz, 2-SC6H4), 7.26 (4H, br. d, 3J=7.0
Hz, 3-SC6H4), 4.52 (1H, br. sept. 3J=5.8 Hz, OCHMe2 cis to
OMe), 4.41 (1H, br. sept. 3J=5.8 Hz, OCHMe2 trans to OMe),
3.93 (2H, s, CH2py), 3.24-2.81 (8H, br. m), 2.37 (6H, s,
C6H4Me), 1.21 (6H, br. d, 3J=6.1 Hz, OCHMe2 cis to OMe),
1.11 (6H, br. d, 3J = 6.0 Hz, OCHMe2 trans to OMe). A
satisfactory 13C NMR spectrum could not be obtained because
of the fluxional nature of the compound. IR: 3453 (w), 1599
(w), 1299 (m), 1143 (w), 1105 (m), 1060 (m), 1024. (w), 962 (w),
939 (m), 829 (w), 669 (w) cm-1. cm-1. Anal. found (calcd. for
(91) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode; Academic Press: New York, 1997.
(92) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(93) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(94) Betteridge, P. W.; Cooper, J. R.; Cooper, R. I.; Prout, K.; Watkin, D.
J. J. Appl. Crystallogr. 2003, 36, 1487.
(95) Sheldrick, G. M.; Schneider, T. R. Methods Enzymol. 1997, 277, 319–
343.

10454 Inorganic Chemistry, Vol. 48, No. 21, 2009
Schwarz et al.
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 para-
meters for all the structures have been deposited at the Cam-
bridge Crystallographic Data Centre. See Notice to Authors,
Issue No. 1.
(6.0 mL) was added, rapidly disolving both solids. The 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).
General Procedure for Polymerization of ε-CL. Parallel du-
plicate experiments were carried out in each of which a solution
of ε-CL (6.6 mmol) in toluene (3.0 mL) was heated to 100 °C and
added to a solution of catalyst (0.066 mmol) in toluene (3.8 mL)
also at 100 °C. For one sample aliquots were taken at the
respective time. Upon completion the reaction was quenched
by addition of wet THF (10 mL), and the solution evaporated to
dryness to give the crude polymer. Isolated yields were obtained
from the parallel experiment for which the polymer was
quenched by wet THF (10 mL) and precipitated by addition
to ethanol (250 mL) with vigorous stirring, filtered and dried to
constant weight in vacuo.
General Procedure for Solventless (Melt) Polymerization of
rac-LA. A Schlenk flask was charged with catalyst and rac-LA
at the desired ratio and heated at 130 °C for 30 min with stirring.
The mixture was cooled to RT, and wet THF (10 mL) was then
added and the resulting solution evaporated to dryness to give
the crude polymer.
Acknowledgment. We thank the EPSRC for support.
Supporting Information Available: X-ray crystallographic
data in CIF format for the structure determinations of 9-15;
additional data concerning the ROP catalysis. This material is
available free of charge via the Internet at http://pubs.acs.org.
General Procedure for Solution Polymerization of rac-LA. rac-
LA (6.00 mmol) and catalyst (0.06 mmol) were added to a
Schlenk flask and heated to 70 °C. To this, hot (70 °C) toluene