Yttrium Phosphasalen Initiators for rac-Lactide Polymerization

Feb 26, 2013 - initiators for the heteroselective ring-opening polymerization ... heterotactic PLA.6−9 There are also three reports of yttrium initi...
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Yttrium Phosphasalen Initiators for rac-Lactide Polymerization Clare Bakewell,†,§ Thi-Phuong-Anh Cao,‡,§ Xavier F. Le Goff,‡ Nicholas J. Long,† Audrey Auffrant,*,‡ and Charlotte K. Williams*,† †

Department of Chemistry, Imperial College London, London SW7 2AZ, U.K. Laboratoire Heteroelements et Coordination, CNRS, Ecole Polytechnique, 91128 Palaiseau Cedex, France

‡

S Supporting Information *

ABSTRACT: A series of highly active yttrium phosphasalen initiators for the heteroselective ring-opening polymerization of rac-lactide are reported. The initiators are yttrium alkoxide complexes ligated by iminophosphorane analogues of the popular “salen” ligand, termed “phosphasalens”. A series of novel phosphasalens have been synthesized, with varying substituents on the phenoxide rings and ethylene, propylene, rac-cyclohexylene, R,R-cyclohexylene, phenylene, and 2,2dimethylpropylene groups linking the iminophosphorane moieties. Changing the substituents on the phosphasalen ligands results in changes to the rates of polymerization (kobs) and to the PLA heterotacticity (Ps = 0.87). Generally, the initiators have high rates, excellent polymerization control, and a tolerance to low loadings.

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diamides, which show high activities and good control.8 By changes in the substituents on the phosphorus atoms it was possible to control the complexes’ nuclearity in THF solutions; mononuclear complexes showed high heteroselectivity (Ps = 0.8), while dinuclear complexes (dimers) lacked any stereocontrol.8e We also discovered that more electron donating substituents led to qualitatively higher rates of polymerization.8d This led to the development and application of electron-donating iminophosphorane analogues of the popular salen ligand class phosphasalens.10 In early 2012, we reported a new phosphasalen yttrium complex, complex A (Scheme 1), for use as an initiator in lactide polymerization.10 It showed rates among the highest reported combined with high heteroselectivity (Ps = 0.9). Complex A is also capable of high activity even at very low catalyst loadings (0.02 mol %) and using

INTRODUCTION The ring-opening polymerization (ROP) of rac-lactide (racLA) is of interest because the product, polylactide (PLA), is a degradable and biocompatible material.1 The monomer, lactide, is obtained from lactic acid, which, in turn, is produced from the fermentation of sugars. Lactide undergoes ring-opening polymerization (ROP) to produce PLA, a process which can be initiated by metal complexes, organo-catalysts, or enzymes.1c,2 Metal alkoxides or amide complexes can be desirable due to their high rates (activities), high selectivities, and facility to use low loadings, thereby producing high-molecular-weight polymers. The selection of the initiator can also influence the polymer tacticity; in particular, controlling the stereochemistry of rac-LA ROP is important.1c,2b,3 Yttrium initiators have attracted considerable attention due to their very high rates of polymerization, high degrees of polymerization control, and facility to control the polymer tacticity via modification of the ancillary ligands. The earliest reports of yttrium initiators focused on homoleptic yttrium alkoxide complexes.4 These showed excellent activities but needed to be prepared in situ to prevent redistribution reactions and/or formation of μ-oxo clusters. Subsequently, a range of ancillary ligands have been widely investigated, including diphenolate diimines/diamines (Salen or Salan ligands),5 amine bis(phenolates),6 dithiaalkane bis(phenolates),7 and bis(phosphinic)diamides,8 as well as a range of other ligands with amido, amidinato, phosphido, and oxazoline donors.9 Some of these successful ligands can be used to effect stereocontrolled ROP of rac-LA, especially to produce heterotactic PLA.6−9 There are also three reports of yttrium initiators which can produce isotactic, stereoblock PLA from rac-LA.9g,h,k We have previously investigated phosphinic © 2013 American Chemical Society

Scheme 1. Structures of Yttrium Phosphasalen Initiators A and B, Which Are Heteroselective and Isoselective for the ROP of rac-LA, Respectively10,11

Special Issue: Recent Advances in Organo-f-Element Chemistry Received: November 26, 2012 Published: February 26, 2013 1475

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The proligands were deprotonated by reaction with 4 equiv of potassium bis(trimethylsilyl)amide; quantitative conversion was verified by 31 P{ 1 H} NMR spectroscopy. Yttrium phosphasalen chloride complexes were formed by reaction with [YCl3(THF)3.5]; this led to a shift to lower field in the singlet signal observed by 31P{1H} NMR spectroscopy (δP ∼30 ppm). Addition of potassium alkoxide (ethoxide/tert-butoxide) to the yttrium halide complexes led to the formation of the yttrium phosphasalen alkoxide compounds 1−6, which, in general, showed a slight upfield shift in 31P{1H} NMR spectra (Scheme 2). All of the complexes were fully characterized by NMR experiments and elemental analyses. In some cases, crystals suitable for X-ray crystal diffraction have been obtained. Compound 6 has recently been communicated,11 but its performance is included here, along with that of compound A,10 for purposes of comparison. X-ray Crystallography. Crystals suitable for single-crystal X-ray diffraction experiments were isolated from a cyclohexane solution of compound 1 (Table 1 and Figure 1). The complex cocrystallized with equal proportions of the (R,R)- and (S,S)1,2-diiminocyclohexylene backbone. Compound 2, synthesized from the resolved (R,R)-1,2-diaminocyclohexane, shows the same structural data as 1 (Figure S1 and Table S1 (Supporting Information)). The yttrium center has an octahedral coordination geometry with the two nitrogen and two oxygen atoms of the phosphasalen ligand occupying the equatorial positions and the tert-butoxide group and a THF molecule occupying the axial positions. The Y−N1,2 bond lengths in complex 1 are closely comparable with those observed in A (Y−N1,2 bond lengths 2.380(7) and 2.391(2) Å for 1 compared with 2.375(2) and 2.324(2) Å for A), and all other bond lengths for complex 1 are similar, within error, to those for A.10 Only the Y−O bonds experience a slight shortening (Y−O bonds 2.234(2) Å for 1 compared with 2.167(2) and 2.170(2) Å for A). On comparison of the structures of complexes 1 and 2 featuring a cyclohexylene linkage with that of A (ethylene linkage), there are differences in the orientation of the phenyl rings attached to the phosphorus atoms which could be due to steric interactions between these rings and the cyclohexylene ring atoms. This steric hindrance may “open” the coordination sphere of yttrium and enable THF coordination at the sixth coordination site. The same rationale may explain why compound 5, which has a 1,2-phenylenediimine linker, also has a coordinated THF molecule (Figure 2 and Table 1). It adopts a distortedoctahedral geometry, with the phosphasalen ligand occupying the equatorial positions and the axial positions being occupied by the tert-butoxide group and a THF molecule. Once again, the Y−O1,2 and Y−N1,2 bond length values are in close agreement with those obtained for complexes A, 1, and 2.10 The phosphasalen ligand with a 2,2-dimethylpropylene diimine backbone would also be expected to be less sterically congested than A, and indeed, compound 4 also has a coordinated THF molecule (Figure 3). The elemental analyses of complexes 1−5 confirm the presence of a THF molecule in the coordination sphere of yttrium, in the solid state, even after prolonged periods of drying. X-ray crystal structures for compounds 1, 2, 4, and 5 also show a bound THF molecule, despite the crystals being grown from cyclohexane solutions. In order to understand whether THF remained coordinated in solution, 1H NMR spectra were recorded in d8-toluene; however, these all showed that the THF resonances were at almost exactly the same chemical shifts as those of free THF. This indicates that THF is

unpurified lactide. Very recently, complex B has been reported, which enables good isoselectivity (Pi = 0.8) while maintaining high rates.11 Thus, the iminophosphorane ligand appears to be useful for this type of catalysis and a greater understanding of the structure−activity relationships is merited. Herein, we describe a series of new yttrium phosphasalen complexes where the groups linking the imino functionalities and/or the phenolate substituent differ. There is an investigation of the underlying influences of the ligand structures on rate and heteroselectivity. In particular, we were motivated to target complexes which would exist as discrete (mononuclear) species in solution, as dinuclear yttrium phosphasalen initiators have earlier been shown to be less efficient.8e,10

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RESULTS AND DISCUSSION Synthesis of Compounds 1−6. To form discrete mononuclear species, bulky substituents at the ortho positions of the phenoxide rings are essential. Thus, tert-butyl substituents at the ortho phenolate positions were used throughout this study. Furthermore, the group linking the two imino groups must be controlled to ensure that only a single yttrium center is coordinated. Therefore, linkers comprising two to three carbons were selected. The proligands L1−L6 were synthesized by reacting 2,4-di-tert-butyl-6-phosphinophenol, via the Kisanov reaction, with bromine and the appropriate diamine (Scheme 2 and Supporting Information). This method gave the phosphasalen proligands L1−L6 in high yields (Scheme 2 and Scheme S1 (Supporting Information)). All of the new compounds were fully characterized by multinuclear NMR spectroscopy and elemental analyses. Scheme 2. General Synthetic Route to Achieving Proligands L1−L6 and Compounds 1−6a

a Reagents and conditions: (i) (a) Br2 (1 equiv), CH2Cl2, 195−298 K, 1 h; (b) DABCO (0.5 equiv), diamine (0.5 equiv), CH2Cl2, 195−298 K, 16 h, yields L1 75%, L2 57%, L3 71%, L4 65%, L5 72%, L6 69%; (ii) (a) KHDMS (4 equiv), THF, 298 K, 4 h, (b) [YCl3(THF)3.5], THF, 298 K, 4 h, (c) KOR′, THF, 298 K, 7 h, yields 1 79%, 2 87%, 3 74%, 4 88%, 4a 81%, 5 87%, 6 88%.

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Table 1. Selected Bond Lengths (Å) and Angles (deg) for Compounds 1, 4, and 6 Y1−O1

Y1−O2

1 4 5

2.234(2) 2.232(3) 2.243(3) O1−Y1−N1

2.234(2) 2.191(3) 2.220(3) N1−Y1−N2

1 4 5

101.47(8) 84.0(1) 80.8(1)

69.9(1) 80.8(1) 68.3(1)

Y1−O3 tBu

Y1−N2

P1−N1

2.058(2) 2.518(2) 2.391(2) 2.391(2) 2.072(3) 2.462(3) 2.432(4) 2.402(4) 2.040(3) 2.467(3) 2.389(4) 2.406(3) N2−Y1−O2 O1−Y1−O2 O2−Y1−O3

Y1−O4 THF

1.588(2) 1.597(4) 1.606(4) O2−Y1−O4

82.17(6) 83.2(1) 80.9(1)

120.1(1) 109.3(1) 126.1(1)

Y1−N1

82.18(5) 95.6(1) 95.5(1)

97.10(6) 78.3(1) 95.5(1)

P2−N2 1.588(2) 1.599(4) 1.604(4) O3−Y1−O4 178.5(1) 173.5(1) 160.6(1)

Figure 1. ORTEP view of the solid-state structure of compound 1. The R,R (a) and S,S (b) enantionmers are both illustrated. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted for clarity.

a slight excess of pyridine and removal of all solvents under vacuum. When the sample was redissolved, the 1H NMR spectrum (d8-toluene) showed that pyridine was present, but again, the resonances were not shifted significantly in comparison to those of free pyridine. Taken together, these findings provide tentative support for the notion that THF is coordinated to the yttrium center for complexes 1−5. In contrast, complex 6 does not have any THF coordinated/ associated with it, either by 1H NMR spectroscopy or by elemental analysis. This is in line with the characterization data for the related compound A. Taking into account its structural similarity to complex A (ethylene backbone), it is proposed that complex 6 also has a pentacoordinate ytrrium center. rac-Lactide Polymerization. Compounds 1−6 were tested as initiators for rac-lactide ring-opening polymerization (Scheme 3, Table 2).

Figure 2. ORTEP view of the structure of compound 5 with thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms are omitted for clarity.

Scheme 3. General Polymerization Procedurea

a

Reagents and conditions: (i) [I]/[LA] = 1/500, THF, 298 K, 1 M [LA].

The polymerizations were conducted under a standard set of conditions, using a 1 M solution of lactide in THF at 298 K. The solvent selection is important: the initiators decompose in methylene chloride solutions, and toluene can only be applied at elevated temperatures (>343 K). The polymerizations were monitored by taking regular aliquots which were analyzed by NMR spectroscopy to determine the conversion and by GPCMALLS (gel permeation chromatography-multiple angle laser light scattering) to determine the evolution of the numberaveraged molecular weight. The polymerization kinetics were monitored for each initiator, showing a first-order dependence

Figure 3. ORTEP view of the solid-state structure of compound 4, with thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms are omitted for clarity.

either not coordinated or that rapid exchange occurs on the NMR time scale. Additional NMR experiments, including lowtemperature studies (243 K) and NOE NMR, failed to provide conclusive evidence of THF coordination. However, it was possible to remove the THF from the complexes by addition of 1477

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Table 2. Polymerization Data Using Initiators 1−6 initiatora I

[LA]0/[I]

time (min)

conversion (%)b

kobs × 10−3 (s−1)c

Mn(exptl) (g mol−1)d

Mn(calcd) (g mol−1)

PDId

Pse

1 1f 2 3 4 4a 5 6 A

500/1 500/1 500/1 500/1 500/1 500/1 500/1 1000/1 1000/1

4 4 4 9 20 22 6 0.33 0.75

89 92 95 86 91 89 90 86 97

9.4 10.7 12.3 3.7 2.0 1.5 6.7

84000 45600 120500 66800 76500 70900 196200 165000 223000

64100 66200 68400 61900 65500 64100 64800 124000 140000

1.05 1.04 1.07 1.07 1.02 1.01 1.05 1.5 1.34

0.75 0.75 0.75 0.67 0.7 0.69 0.84 0.87 0.86

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a

Polymerization conditions: THF, 298 K, 1 M [LA]. bDetermined by integration of the methine region of the 1H NMR spectrum (LA 4.98−5.04 ppm; PLA 5.08−5.22 ppm). cDetermined from the gradients of the plots of ln{[LA]0/[LA]t} versus time, where the average errors are 5−12% (determined using initiators 4a and 5). dDetermined by gel permeation chromatography (GPC) in THF, using multiangle laser light scattering (gel permeation chromatography-multiple angle laser light scattering, GPC-MALLS; see the Experimental Section). eDetermined by analysis of all the tetrad signals in the methine region of the homonuclear decoupled 1H NMR spectrum.12 fPolymerization conducted with 1 equiv of iPrOH.

contrast to previous results from our group using bis(phosphinic)diamido yttrium initiators, where C3-bridged complexes were significantly faster than C2-bridged analogues.8c Okuda has discovered that for the dithia bis(phenoxide) yttrium initiators C3-bridged complexes are both faster and more heteroselective; this was attributed to increased ligand flexibility, facilitating configurational isomerization.7c,e Aluminum salan complexes also showed enhanced selectivities and rate with C3 vs C2 bridging groups.14 Polymerization Control. All polymerizations showed a linear evolution of Mn against conversion and narrow polydispersity indices, indicative of good control. The C3bridged compounds showed Mn values closer to those predicted on the basis of initiator concentration (Figure 5). In contrast, C2-bridged compounds (1, 2, and 5) showed molecular weights higher than predicted. This is attributed to the qualitatively higher rates for the C2-bridged initiators combined with the reduced initiating capability of the tertbutoxide group (note both 6 and A, which are significantly faster, still show further reduced control). When 1 equiv of isopropyl alcohol is added to these reactions, the Mn values match much more closely those predicted on the basis of initial monomer concentration (Table 2, line 2); this finding confirms that the lack of control relates to the poor initiating ability of the sterically congested tert-butyl alkoxide. Nevertheless, the rate of propagation is consistently faster than the rate of initiation, leading to products with narrow PDI in all cases. All of the new initiators are heteroselective, but the degree of stereocontrol is reduced according to the nature of the diimine linker group; i.e., A > 6 > 5 > 1 = 2 > 4 > 3. The tacticity is controlled by a chain end control mechanism, whereby the stereochemistry of the last inserted monomer unit controls the binding/ring opening of the subsequent lactide unit. Such heteroselectivity is rather unusual for this type of yttrium complex, as related salen/salan yttrium initiators show little or no heteroselectivity (Ps < 0.7).5a,c,d,g,h It is proposed that the stereocontrol may arise from the increased steric shielding of the active site by the iminophosphorane group, in particular from the two phenyl substituents on the phosphorus atoms. A possible rationale for the stereoselectivity might relate to the differing degrees of steric crowding of the active sites: more open active sites, such as those where THF is coordinated in the solid state, show lower degrees of control vs more congested active sites, where THF remains unbound, e.g. A and 6. We, and others, have previously observed that the rates and

on lactide concentration in every case; the pseudo-first-order rate constants, kobs, were obtained as the gradient of the linear fits to plots of ln([LA]0/[LA]t) versus time (Figure 4). The tacticity of the resulting PLA was assessed by integration of the methyne region of the homonuclear decoupled proton NMR spectrum and by application of Bernoullian statistics to predict the tetrad probabilities, according to the method described by Coudane et al.12 Compounds 1−6 were all highly active initiators in the ROP of rac-LA (Table 2). Initiator 6, which is structurally analogous to compound A, was extremely active toward the ROP of racLA, with the polymerization proceeding to nearly full conversion in A ≫ 2 > 1 > 5 > 3 > 4, 4a. It is pertinent to consider the different structures of compounds A and 6 vs 1−5, as these account for the largest differences in rate. All of the complexes exhibit mononuclear structures in the solid state and in solution; however, initiators A and 6 have pentacoordinate, squarepyramidal geometries at yttrium, while 1−5 have hexacoordinate, octahedral geometries at yttrium, with a molecule of THF coordinated. These differing coordination geometries may account for the stark differences in rate between A and 6 and 1−5. Within the series of hexacoordinate yttrium complexes 1− 5, those with C2 bridge groups are faster. This finding is in 1478

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Figure 4. Plots of ln([LA]0/[LA]t) vs time: (i) initiators 1−3 and 5; (ii) initiators 4 and 4a. Conditions: [LA]0 = 1 M, 1/500 [I]/[LA], THF, 298 K.

Ps = 0.69 (toluene) vs 0.75 (THF) and Ps = 0.67 (toluene) vs 0.84 (THF), respectively. It is worth highlighting that this result is less likely due to the slurry conditions, as when identical experiments were conducted with the highly isoselective compound B, identical stereoselectivities were observed (Pi = 0.76, 298 K, in both toluene and THF). This finding suggests that high heteroselectivity depends both on the ligand substituents and on the use of THF as the solvent. This could be due to THF coordination accelerating coordination/ insertion of a particular enantiomer of rac-lactide. However, other physical/chemical phenomena could also be implicated: e.g., differences in solvent polarity. This solvent dependence will be the subject of further, future investigations.

stereocontrol are higher when polymerizations are conducted in THF in comparison to other solvents.1c,2d,6o,q,7b,c,8a,e,h,9c These phosphasalen initiators also show reduced heteroselectivity using toluene, at 348 K, as the reaction medium. For example, initiator 4a has a Ps value of 0.60 in toluene versus 0.69 in THF. The observed rates cannot, however, be easily compared due to the difference in temperature required for homogeneous polymerizations in toluene: 348 K (toluene) versus 298 K (THF). In order to compare the polymerizations at the same temperature, slurry phase polymerizations, in toluene, were conducted at 298 K; here the reaction was heterogeneous at the start of the polymerization but became homogeneous as the polymerization progressed. This is attributed to the enhanced solubility of PLA in toluene (298 K) in comparison to raclactide (298 K). Under slurry conditions, a marked reduction in heteroselectivity was observed for compounds 1 and 5, where 1479

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Figure 5. Evolution of Mn versus percentage conversion for the polymerization using initiator 4 (circles) and initiator 4a (squares) and PDI versus percentage conversion of initiator 4a (diamonds). Conditions: [LA]0 = 1 M, 1/500 [I]/[LA], THF, 298 K.

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prepared following literature procedure.15 Ligand syntheses are described in the Supporting Information. Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker Av300 spectrometer operating at 300 MHz for 1H, 75.5 MHz for 13C{1H}, and 121.5 MHz for 31P{1H}. Solvent peaks were used as internal references for 1H and 13C chemical shifts (ppm). 31P peaks were referenced to external 85% H3PO4. When needed, higher resolution 31P{1H} NMR and 1H{1H} NMR (homodecoupled spectroscopy) experiments were performed on a Bruker Av500 spectrometer, equipped with a z-gradient bbo/5 mm tunable probe and a BSMS GAB 10 A gradient amplifier providing a maximum gradient output of 5.35 G/cmA. 1H NMR spectra for all lactide polymerizations were performed on a Bruker Av400 instrument. Elemental analyses were determined by Mr. Stephen Boyer at London Metropolitan University, Science Centre. PLA number averaged molecular weights, Mn, and polydispersity indexes (Mw/Mn; PDI) were determined using gel permeation chromatography, conducted on a Polymer Laboratories GPC-50 instrument equipped with multiangle laser light scattering (GPC-MALLS). Two Polymer Laboratories Mixed D columns were used in series, with THF as the eluent, at a flow rate of 1 mL min−1 at 35 °C. The light scattering detector was a triple-angle detector (Dawn 8, Wyatt Technology), and the data were analyzed using Astra V version 5.3.4.18. The refractive angle increment for polylactide (dn/dc) in THF was 0.042 mL g−1.16 General Procedure for the Synthesis of the Yttrium Complexes 1−6. Potassium bis(trimethylsilyl)amide (240 mg, 1.2 mmol) was added into a slurry of the phosphasalen proligands Lx (0.30 mmol) in THF (20 mL). After 4 h, a cloudy solution was obtained. The completion of the deprotonation reaction was verified by 31P{1H} NMR spectroscopy. The insoluble potassium salt was removed by centrifugation, and [YCl3(THF)3.5] (134 mg, 0.30 mmol) was added. After 4 h of stirring at 298 K, potassium tert-butoxide (34 mg, 0.30 mmol) was added into the mixture, giving a cloudy solution. Stirring was continued for 7 h, and the solid was removed by centrifugation. The solvent was evaporated in vacuo, and the residue was crystallized in cyclohexane (5 mL), giving 1−5 as colorless crystals or solids. Compound 1: L1 (316 mg, 0.30 mmol); 31P{1H} NMR spectrum after deprotonation δ 18 ppm, after the addition of [YCl3(THF)3.5] δ 22.6 ppm, 27.5 ppm (equal intensities); yield 265 mg (2.4 mmol,

CONCLUSIONS A series of phosphasalen yttrium alkoxide compounds, 1−6, were synthesized and characterized. All compounds were fully characterized by multinuclear NMR spectroscopy and elemental analysis and, in some cases, X-ray diffraction. The complexes show mononuclear structures in both the solid state (X-ray diffraction) and solution (31P, 13C NMR spectroscopic interpretation). All new compounds are viable initiators for raclactide ROP, showing very high rates. Within the series of phophasalen ligands, the more electron donating ligand shows the highest rate and the diimine linker group also influences the rate in the order ethylene > cyclohexylene > phenylene > propylene. The initiators exhibit good polymerization control, with a linear evolution of molecular weight and narrow polydispersity indices being observed in all cases. The degree of molecular weight control improves in the inverse order to rate. The initiators all yield heterotactic PLA from rac-LA; the Ps values decrease according to the nature of the diimine linker group in the order ethylene > cyclohexylene > phenylene > propylene. Thus, the fastest initiators are also the most heteroselective. It is proposed that these factors are both controlled by the steric congestion at the active site, which can be easily tuned by modification of the phosphasalen ancillary ligand.

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EXPERIMENTAL SECTION

Materials and Methods. All reactions were conducted under an atmosphere of dry nitrogen or argon, using standard Schlenk and glovebox techniques. Solvents and reagents were obtained from commercial sources. Tetrahydrofuran, toluene, pentane, hexane, and petroleum ether were distilled from sodium/benzophenone, under dry nitrogen. Dichloromethane was distilled from CaH2, under dry nitrogen. Tetrahydrofuran and petroleum ether for ligand and complex synthesis were directly taken from a MBraun MB-SPS 800 Solvent Purification Machine. rac-Lactide was recrystallized from anhydrous toluene and sublimed three times prior to use. [YCl3(THF)3.5] was 1480

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Organometallics

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79%); 1H NMR (300 MHz, THF-d8; δ (ppm)) 7.89 (ddd, 3JP,H =10.6 Hz, 3JH,H= 7.5 Hz, 4JH,H= 1.0 Hz, 2H, o-CH(PPh2)), 7.75 (ddd, 3JP,H = 12.3 Hz, 3JH,H = 7.5 Hz, 4JH,H = 1.0 Hz, 2H, o-CH(PPh2)), 7.62 (ddd, 3 JP,H = 11.2 Hz, 3JH,H = 7.5 Hz, 4JH,H = 1.0 Hz, 2H, o-CH(PPh2)), 7.56 (ddd, 3JP,H = 11.0 Hz, 3JH,H = 7.5 Hz, 4JH,H = 1.0 Hz, 2H, oCH(PPh2)), 7.51−7.42 (m, 5H, p-CH(PPh2) + m-CH(PPh2)), 7.38 (m, 2H, m-CH(PPh2)), 7.32 (m, 2H, m-CH(PPh2)), 7.27 (d, 4JH,H = 2.0 Hz, 1H, CbH), 7.21 (d, 4JH,H = 2.0 Hz, 1H, CbH), 7.17 (m, 1H, pCH(PPh2)), 6.84 (dd, 4JH,H = 2.0 Hz, 3JP,H = 16.0 Hz, 1H, CdH), 6.82 (m, 2H, m-CH(PPh2)), 6.47 (dd, 4JH,H = 2.0 Hz, 3JP,H = 16.0 Hz, 1H, CdH), 4.62 (m, 1H, N-CH-CH-N), 2.97 (m, 4JP,H = 3.0 Hz, 1H, NCH-CH-N), 1.57 (m, 2H, CH2(cyclohexane)), 1.31 (s, 9H, Cc,aIVCIV(CH3)3), 1.12 (m, 2H, CH2(cyclohexane)), 1.12 (s, b, 9H, O− CIV(CH3)3), 1.10 (s, 9H, Cc,aIV- CIV(CH3)3), 1.09 (s, 9H, Cc,aIVC IV (CH 3 ) 3 ), 0.96 (s, 9H, C c,a IV -C IV (CH 3 ) 3 ), 0.82 (m, 2H, CH2(cyclohexane)), 0.66 (m, 1H, CH2(cyclohexane)), 0.48 (m, 1H, CH2(cyclohexane)); 31P{1H} NMR (121.5 Hz, THF-d8; δ(ppm)): 27.6 (s, PV), 20.8 (s, PV); 13C{1H} NMR (75 MHz, THF-d8; δ (ppm)) δ 169.1 (m, CIV-O), 168.7 (m, CIV-O), 140.1 (d, 3JP,C = 8.0 Hz, CcIV), 139.5 (d, 3JP,C = 8.0 Hz, CcIV),137.3 (d, 1JP,C = 83.2 Hz, CIV(PPh2)), 137.1 (d, 1JP,C = 85.5 Hz, CIV(PPh2)), 134.9 (d, 3JP,C = 13.5 Hz, CaIV), 135.2 (d, 2/3JP,C= 9.0 Hz, m-or o-CH(PPh2)), 134.4 (d, 2/3JP,C= 9.0 Hz, m-or o-CH(PPh2)), 134.0 (d, 2/3JP,C = 8.2 Hz, m-or o-CH(PPh2)); 133.9 (d, 2/3JP,C = 8.2 Hz, m-or o-CH(PPh2)), 133.8 (d, 3JP,C = 14.3 Hz, CaIV), 132.4 (d, 1JP,C = 86.2 Hz, CIV(PPh2)), 132.1 (d, 4JP,C = 2.1 Hz, p-CH(PPh2)), 132.0 (d, 4JP,C = 2.2 Hz, p-CH(PPh2)), 131.9 (d, 4 J P,C = 2.2 Hz, p-CH(PPh 2 )), 131.8 (d, 1 J P,C = 87.0 Hz, CIV(PPh2)),129.2 (d, 2/3JP,C = 11.2 Hz, m-or o-CH(PPh2)), 129.1 (d, 2/3 JP,C = 11.2 Hz, m-or o-CH(PPh2)), 128.9 (d, 2/3JP,C = 11.2 Hz, m-or o-CH(PPh2)), 128.8 (d, 2JP,C = 11.8 Hz, CdH), 128.6 (s, CbH), 128.3 (s, CbH), 127.6 (d, 2JP,C = 13.5 Hz, CdH), 116.0 (d, 1JP,C = 118.4 Hz, CIV(PPh2)), 113.2 (d, 1JP,C = 118.4 Hz, CIV(PPh2)), 61.3 (br s, N-CHCH-N), 54.0 (s, CH2(cyclohexane ring)), 49.0 (s, CH2(cyclohexane ring)), 36.1 (s, CIV(CH3)3), 35.9 (s, CIV(CH3)3), 34.9 (s, CIV(CH3)3), 34.6 (s, CIV(CH3)3), 32.2 (s, CIV(CH3)3), 32.0 (s, CIV(CH3)3), 30.2 (s, CIV(CH3)3). Anal. Calcd for C66H87N2O4P2Y: C, 70.57; H, 7.81; N, 2.49. Found: C, 70.66; H, 7.65; N, 2.59. Compound 2: L2 (316 mg, 0.30 mmol); 31P{1H} NMR spectrum after deprotonation δ 18 ppm, after addition of [YCl3(THF)3.5] δ 22.6 ppm, 27.5 ppm (equal intensities); yield 293 mg (0.26 mmol, 87%); 1 H NMR (300 MHz, THF-d8; δ (ppm)) 7.89 (ddd, 3JP,H = 10.6 Hz, 3 JH,H = 7.5 Hz, 4JH,H = 1.0 Hz, 2H, o-CH(PPh2)), 7.75 (ddd, 3JP,H = 12.3 Hz, 3JH,H = 7.5 Hz, 4JH,H = 1.0 Hz, 2H, o-CH(PPh2)), 7.62 (ddd, 3 JP,H = 11.2 Hz, 3JH,H = 7.5 Hz, 4JH,H = 1.0 Hz, 2H, o-CH(PPh2)), 7.56 (ddd, 3JP,H = 11.0 Hz, 3JH,H = 7.5 Hz, 4JH,H = 1.0 Hz, 2H, oCH(PPh2)), 7.51−7.42 (m, 5H, p-CH(PPh2) + m-CH(PPh2)), 7.38 (m, 2H, m-CH(PPh2)), 7.32 (m, 2H, m-CH(PPh2)), 7.27 (d, 4JH,H = 2.0 Hz, 1H, CbH), 7.21 (d, 4JH,H = 2.0 Hz, 1H, CbH), 7.17 (m, 1H, pCH(PPh2)), 6.84 (dd, 4JH,H = 2.0 Hz, 3JP,H = 16.0 Hz, 1H, CdH), 6.82 (m, 2H, m-CH(PPh2)), 6.47 (dd, 4JH,H = 2.0 Hz, 3JP,H = 16.0 Hz, 1H, CdH), 4.62 (m, 1H, N-CH-CH-N), 2.97 (m, 1H, N-CH-CH-N), 1.57 (m, 2H, CH2(cyclohexane)), 1.31 (s, 9H, Cc,aIV-CIV(CH3)3), 1.12 (m, 2H, CH2(cyclohexane)), 1.12 (s, b, 9H, O-CIV(CH3)3), 1.10 (s, 9H, Cc,aIV-CIV(CH3)3), 1.09 (s, 9H, Cc,aIV-CIV(CH3)3), 0.96 (s, 9H, Cc,aIVCIV(CH3)3), 0.82 (m, 2H, CH2(cyclohexane)), 0.66 (m, 1H, CH2(cyclohexane)), 0.48 (m, 1H, CH2(cyclohexane)); 31P{1H} NMR (121.5 MHz, THF-d8; δ(ppm)) 27.6 (s, PV), 20.8 (s, PV); 13 C{1H} NMR (75 MHz, THF-d8; δ (ppm)) 169.1 (m, CIV-O), 140.1 (d, 3JP,C = 8.0 Hz, CcIV), 134.0 (d, 2/3JP,C = 8.2 Hz, m-or o-CH(PPh2)); 133.9 (d, 2/3JP,C = 8.2 Hz, m-or o-CH(PPh2)), 133.8 (d, 3JP,C = 14.3 Hz, CaIV), 132.4 (d, 1JP,C = 86.2 Hz, CIV(PPh2)), 132.0 (d, 4JP,C = 2.2 Hz, p-CH(PPh2)), 131.9 (d, 4JP,C = 2.2 Hz, p-CH(PPh2)), 131.8 (d, 1 JP,C = 87.0 Hz, CIV(PPh2)), 129.2 (d, 2/3JP,C = 11.2 Hz, m-or oCH(PPh2)), 129.1 (d, 2/3JP,C = 11.2 Hz, m-or o-CH(PPh2)), 128.6 (s, CbH), 127.6 (d, 2JP,C = 13.5 Hz, CdH), 113.2 (d, 1JP,C = 118.4 Hz, CIV(PPh2)), 61.3 (br s,, N-CH-CH-N), 54.0 (s, CH2(cyclohexane ring)), 49.0 (s, CH2(cyclohexane ring)), 34.9 (s, CIV(CH3)3), 34.6 (s, CIV(CH3)3), 32.2 (s, CIV(CH3)3), 32.0 (s, CIV(CH3)3), 30.2 (s,

CIV(CH3)3). Anal. Calcd for C66H87N2O4P2Y: C, 70.57; H, 7.81; N, 2.49. Found: C, 70.47; H, 7.97; N, 2.53. Compound 3: L3 (304 mg, 0.30 mmol); 31P{1H} NMR spectrum after the deprotonation δ 23.8 ppm, after the addition of [YCl3(THF)3.5] δ 36.9 ppm; yield 240 mg (0.22 mmol, 74%); 1H NMR (300 MHz, THF-d8; δ (ppm)) 7.63 (dd, 3JH,H = 7.0 Hz, 3JP,H = 10.5 Hz, 4H, o-CH(PPh2)), 7.50 (dd, 3JH,H = 7.0 Hz, 3JP,H = 10.5 Hz, 4H, o-CH(PPh2)), 7.48 (m, 2H, p-CH(PPh2)), 7.41 (m, 4H, mCH(PPh2)), 7.40 (m, 2H, p-CH(PPh2)), 7.32 (m, 4H, m-CH(PPh2)), 7.29 (d, 4JH,H = 2.5 Hz, 2H, CbH), 6.37 (dd, 4JH,H = 2.5 Hz, 3JP,H = 15.5 Hz, 2H, CdH), 3.51 (m, 2H, N-CH2-CH2-CH2-N), 3.16 (m, 2H, NCH2-CH2-CH2-N), 1.90 (m, 1H, N-CH2-CH2-CH2-N), 1.63 (m, 1H, N-CH2-CH2-CH2-N), 1.42 (s, 18H, C(CH3)3), 1.09 (s, 18H, C(CH3)3), 0.86 (s, 9H, O−C(CH3)3); 31P{1H} NMR (121.5 MHz, THF-d8; δ (ppm)) 33.8 (s); 13C{1H} NMR (75 MHz, THF-d8; δ (ppm)) 169.3 (d, 3JP,C = 1.5 Hz, CIV-O), 139.0 (d, 3JP,C = 8.0 Hz, Cc,aIV), 134.3 (d, 2/3JP,C = 9.0 Hz, m-or o-CH(PPh2)), 134.1 (d, 2/3JP,C = 9.0 Hz, m-or o-CH(PPh2), 133.9 (d, 3JP,C = 10.5 Hz, Cc,aIV), 132.6 (d, 1 JP,C = 87.8 Hz, CIV-PPh2), 131.9 (d, 4JP,C = 1.0 Hz, p-CH(PPh2)), 131.8 (d, 4JP,C = 1.0 Hz, p-CH(PPh2)), 128.9 (d, 2/3JP,C = 11.5 Hz, mor o-CH(PPh2)), 128.4 (s, CbH), 128.1 (d, 2JP,C = 14.0 Hz, CdH), 113.3 (d, 1JP,C = 121.0 Hz, CIV(PPh2)), 69.8 (s, O-CIV(CH3)3), 47.1 (d, 2 JP,C = 7.0 Hz, N-CH2-CH2-CH2-N), 36.4 (t, 3JP,C = 9.0 Hz, N-CH2CH2-CH2-N), 34.6 (s, O-CIV(CH3)3), 31.9 (s, Cc,aIV-CIV(CH3)3), 31.7 (s, Cc,aIV-CIV(CH3)3), 31.4 (s, Cc,aIV-CIV(CH3)3), 30.4 (s, Cc,aIVCIV(CH3)3). Anal. Calcd for C63H83N2O4P2Y: C, 69.86; H, 7.72; N, 2.59. Found: C, 69.72; H, 7.66; N, 2.67. Compound 4: L4 (312 mg, 0.30 mmol); 31P{1H} NMR spectrum after the deprotonation δ 22.3 ppm, after the addition of [YCl3(THF)3.5] δ 36.5 ppm; yield 295 mg (0.26 mmol, 88%); 1H NMR (300 MHz, THF-d8; δ (ppm)) 7.70 (ddd, 4JH,H = 1.5 Hz, 3JH,H = 8.0 Hz, 3JP,H = 10.5 Hz, 4H, o-CH(PPh2)), 7.49 (ddd, 4JH,H = 1.5 Hz, 3 JH,H = 8.0 Hz, 3JP,H = 10.5 Hz, 4H, o-CH(PPh2)), 7.42 (m, 4H, mCH(PPh2)), 7.34 (m, 4H, m-CH(PPh2)), 7.29 (d, 4JH,H = 2.0 Hz, 2H, CbH), 7.15 (m, 2H, p-CH(PPh2)), 7.07 (m, 2H, p-CH(PPh2)), 6.43 (dd, 4JH,H = 2.0 Hz, 3JP,H = 15.5 Hz, 2H, CdH), 3.39 (d, 3JP,H = 12.5 Hz, 1H, N−CH2), 3.34 (d, 3JP,H = 12.5 Hz, 1H, N−CH2), 2.85 (d, 3 JP,H = 12.0 Hz, 1H, N-CH2), 2.79 (d, 3JP,H = 12.5 Hz, 1H, N-CH2), 1.36 (s, 18H, Cc,aIV-CIV(CH3)3), 1.02 (s, 18H, Cc,aIV-CIV(CH3)3), 0.80 (s, 9H, O-CIV(CH3)3), 0.62 (s, 3H, N-CH2-CIV(CH3)2), 0.50 (s, 3H, N-CH2-CIV(CH3)2); 31P{1H} NMR (121.5 MHz, THF-d8; δ (ppm)) 33.4 (s); 13C{1H} NMR (75 MHz, THF-d8; δ (ppm)) 169.8 (m, CIVO), 137.9 (d, 3JP,C = 7.7 Hz, Cc,aIV), 133.8 (d, 2/3JP,C = 8.5 Hz, m-or oCH(PPh2)), 133.6 (d, 2/3JP,C = 8.5 Hz, m-or o-CH(PPh2)), 132.8 (d, 1 JP,C = 97.0 Hz, CIV(PPh2)), 131.7 (d, 1JP,C = 87.4 Hz, CIV(PPh2)), 130.9 (s, p-CH(PPh2)), 130.8 (s, p-CH(PPh2)), 127.9 (d, 2/3JP,C = 11.0 Hz, m-or o-CH(PPh2)), 128.8 (d, 2/3JP,C = 11.0 Hz, m-or oCH(PPh2)), 127.5 (s, CbH), 127.5 (d, 2JP,C = 12.5 Hz, CdH), 112.4 (d, 1JP,C = 121.0 Hz, CIV-PPh2), 69.2 (s, O-CIV(CH3)3), 58.1 (d, 2JP,C = 7.5 Hz, N-CH2), 38.1 (t, 3JP,C = 12.5 Hz, N-CH2-CIV-CH2-N), 35.1 (s, Cc,aIV-CIV(CH3)3), 33.7 (s, O-CIV(CH3)), 33.5 (s, Cc,aIV-CIV(CH3)3), 31.0 (s, Cc,aIV-CIV(CH3)3), 29.6 (s, Cc,aIV-CIV(CH3)3), 26.1 (s, C IV (CH 3 ) 2 ), 25.2 (s, N-CH 2 -C IV (CH 3 ) 2 ). Anal. Calcd for C65H86N2O4P2Y: C, 70.32; H, 7.81; N, 2.52. Found: C, 70.40; H, 7.74; N, 2.61. Compound 4a: L4 (312 mg, 0.30 mmol), KOEt (25.2 mg, 0.3 mmol) was used instead of KOtBu; 31P{1H}NMR spectrum after deprotonation δ 22.3 ppm, after addition of [YCl3(THF)3.5] δ 36.5 ppm; yield 265 mg (0.25 mmol, 81%); 1H NMR (300 MHz, THF-d8; δ (ppm)): 7.75 (ddd, 4JH,H = 1.5 Hz, 3JH,H = 7.0 Hz, 3JP,H = 11.5 Hz, 4H, o-CH(PPh2)), 7.58 (ddd, 4JH,H = 1.5 Hz, 3JH,H = 7.0 Hz, 3JP,H = 11.5 Hz, 4H, o-CH(PPh2)), 7.45 (m, 8H, m-CH(PPh2) + pCH(PPh2)), 7.35 (d, 4JH,H = 2.0 Hz, 2H, CbH), 7.33 (vtd, 4JP,H = 2.5 Hz, 3JH,H = 3J′H,H = 7.0 Hz, 4H, m-CH(PPh2)), 6.77 (dd, 4JH,H = 2.0 Hz, 3JP,H = 15.0 Hz, 2H, CdH), 4.03 (t, 3JH,H = 6.0 Hz, 1H, O-CH2CH3), 4.01 (t, 3JH,H = 6.0 Hz, 1H, O-CH2-CH3), 3.69 (d, 3JP,H= 15.0 Hz, 1H, N-CH2), 3.64 (d, 3JP,H = 15.0 Hz, 1H, N-CH2), 2.68 (d, 3JP,H = 12.5 Hz, 1H, N-CH2), 2.61 (d, 3JP,H = 12.5 Hz, 1H, N-CH2), 1.29 (s, 18H, Cc,aIV-CIV(CH3)3), 1.19 (s, 18H, Cc,aIV-CIV(CH3)3), 0.90 (m, 3H, 1481

dx.doi.org/10.1021/om301129k | Organometallics 2013, 32, 1475−1483

Organometallics

Article

O-CH2-CH3), 0.46 (s, 3H, N-CH2-CIV(CH3)2), 0.44 (s, 3H, N-CH2CIV(CH3)2); 31P{1H} NMR (121.5 MHz, THF-d8; δ (ppm)) 33.4 (s); 13 C{1H} NMR (75 MHz, THF-d8; δ (ppm)) 169.1 (m, CIV-O), 139.0 (d, 3JP,C = 7.5 Hz, Cc,aIV), 134.8 (d, 2/3JP,C = 9.0 Hz, m-or o-CH(PPh2)), 134.3 (d, 2/3JP,C = 9.0 Hz, m-or o-CH(PPh2)), 134.0 (d, 3JP,C = 14.5 Hz, Cc,aIV), 133.1 (d, 1JP,C = 88.5 Hz, CIV(PPh2)), 131.7 (d, 1JP,C = 90.5 Hz, CIV(PPh2)), 131.7 (s, p-CH(PPh2) + CbH), 127.9 (d, 2JP,C = 13.0 Hz, CdH), 114.4 (d, 1JP,C = 120.0 Hz, CIV-PPh2), 61.6 (s, O-CH2-CH3), 58.2 (d, 2JP,C = 7.5 Hz, N-CH2), 37.5 (t, 3JP,C = 12.5 Hz, N-CH2-CIVCH2-N), 34.9 (s, Cc,aIV-CIV(CH3)3), 33.5 (s, Cc,aIV-CIV(CH3)3), 31.3 (s, O-CH2-CH3), 30.9 (s, Cc,aIV-CIV(CH3)3), 29.3 (s, Cc,aIV-CIV(CH3)3), 26.2 (s, CIV(CH3)2), 22.3 (s, N-CH2-CIV(CH3)2). Anal. Calcd for C63H82N2O4P2Y: C, 69.92; H, 7.64; N, 2.59. Found: C, 69.96; H, 7.66; N, 2.65. Compound 5: L5 (314 mg, 0.30 mmol); 31P{1H} NMR spectrum after deprotonation δ 13.2 ppm, after addition of [YCl3(THF)3.5] δ 27.3 ppm; yield 290 mg (0.26 mmol, 87%); 1H NMR (300 MHz, THF-d8; δ (ppm)): 7.71 (ddd, 4JH,H = 1.5 Hz, 3JH,H = 8.0 Hz, 3JP,H = 12.0 Hz, 4H, o-CH(PPh2)), 7.58 (ddd, 4JH,H = 1.5 Hz, 3JH,H = 8.0 Hz, 3 JP,H = 12.0 Hz, 4H, o-CH(PPh2)), 7.58 (m, 2H, p-CH(PPh2)), 7.51 (m, 4H, m-CH(PPh2)), 7.45 (m, 2H, p-CH(PPh2)), 7.31 (d, 4JH,H = 3.0 Hz, 2H, CbH), 7.30 (m, 4H, m-CH(PPh2)), 6.37 (dd, 4JH,H = 3.0 Hz, 3JP,H = 15.5 Hz, 2H, CdH), 6.27 (ddd, 3JH,H = 6.0 Hz, 4JH,H = 3.5 Hz, 4JP,H = 3.0 Hz, 2H, CeH), 6.01 (dd, 3JH,H = 6.0 Hz, 4JH,H = 3.5 Hz, 2H, CfH), 1.27 (s, 18H, Cc,aIV-CIV(CH3)3), 1.04 (s, 18H, Cc,aIVCIV(CH3)3), 0.56 (b, 9H, O-CIV(CH3)3); 31P{1H} NMR (121.5 MHz, THF-d8; δ (ppm)) 24.9 (s); 13C{1H} NMR (75 MHz, THF-d8; δ (ppm)) 170.1 (br s, CIV-O), 144.8 (dd, 2JP,C = 19.0 Hz, 3JP,C = 4.0 Hz, CIV-N), 139.0 (d, 3JP,C = 7.5 Hz, Cc,aIV), 134.4 (d, 3JP,C = 16.0 Hz, Cc,aIV), 134.0 (d, 2/3JP,C= 10.0 Hz, m-or o-CH(PPh2)), 132.3 (s, pCH(PPh2)), 132.0 (s, p-CH(PPh2)), 132.0 (d, 1JP,C = 88.5 Hz, CIV(PPh2)), 131.1 (d, 1JP,C = 87.0 Hz, CIV(PPh2)), 129.3 (d, 2/3JP,C = 11.5 Hz, m-or o-CH(PPh2)), 128.8 (s, CbH), 128.7 (d, 2/3JP,C = 11.5 Hz, m-or o-CH(PPh2)), 128.4 (d, 2JP,C = 14.0 Hz, CdH), 122.2 (d, 3JP,C = 10.0 Hz, CeH), 118.3 (s, Cf H), 114.8 (d, 1JP,C = 124.0 Hz, CIV-PPh2), 35.7 (s, Cc,aIV-CIV(CH3)3), 34.3 (s, Cc,aIV-CIV(CH3)3), 33.9 (b, OCIV(CH3)3), 31.8 (s, (b, O-CIV(CH3)3), 31.7 (s, Cc,aIV-CIV(CH3)3), 30.3 (s, Cc,aIV-CIV(CH3)3). Anal. Calcd for C66H80N2O4P2Y: C, 71.02; H, 7.22; N, 2.51. Found: C, 70.85; H, 7.43; N, 2.55. Compound 6: 11 L6 (295 mg, 0.30 mmol); the 31P{1H} NMR spectrum after deprotonation showed only one singlet at +20.3 ppm; the product was isolated as colorless crystals; yield 250 mg (0.26 mmol, 88%);11 1H NMR (300 MHz, THF-d8; δ (ppm)) 7.63 (dd, 3JP,H = 11.5 Hz, 3JH,H = 7.0 Hz, 4H, o-CH(PPh2)), 7.54 (m, 2H, pCH(PPh2)), 7.48 (m, 5H, p-CH(PPh2) + m-CH(PPh2)), 7.40 (dd, 3 JP,H = 11.5 Hz, 3JH,H = 7.0 Hz, 4H, o-CH(PPh2)), 7.39 (m, 1H, mCH(PPh2)), 6.92 (d, 4JH,H = 3.0 Hz, 2H, CbH), 5.94 (dd, 3JP,H = 15.5 Hz, 4JH,H = 3.0 Hz, 2H, CdH), 3.35 (s, 6H, -OCH3), 3.31 (m, 2H, NCH2-CH2-N), 3.18 (m, b, 2H, N-CH2-CH2-N), 1.39 (s, 18H, CaIVCIV(CH3)3), 0.84 (s, b, 9H, O-CIV(CH3)3); 31P{1H} NMR (121.5 MHz, THF-d8; δ (ppm)) 31.6 (s); 13C{1H} NMR (75 MHz, THF-d8; δ (ppm)) 168.8 (br s, CIV-O), 148.2 (d, 3JP,C = 20.0 Hz, CcIV), 141.1 (d, 3JP,C = 9.5 Hz, CaIV), 134.1 (d, 2JP,C = 9.0 Hz, o-CH(PPh2)), 133.6 (d, 2JP,C = 9.0 Hz, o-CH(PPh2)), 132.3 (d, 1JP,C = 88.0 Hz, CIV(PPh2)), 132.0 (d, 4JP,C = 1.5 Hz, p-CH(PPh2)), 131.7 (d, 1JP,C = 90.0 Hz, CIV(PPh2)), 131.7 (d, 4JP,C = 1.5 Hz, p-CH(PPh2)), 129.0 (d, 3JP,C= 10.5 Hz, m-CH(PPh2)), 128.9 (d, 3JP,C = 10.5 Hz, m-CH(PPh2)), 120.3 (d, 4JP,C = 1.0 Hz, CbH), 114.2 (d, 2JP,C = 14.5 Hz, CdH), 111.6 (d, 1JP,C = 123.0 Hz, CIV-PPh2), 55.5 (s, O-CH3), 52.1 (dd, 2/3JP,C = 6.5 Hz, 3/3JP,C = 18.0 Hz, N-CH2-CH2-N), 35.7 (s, CaIV-CIV(CH3)3), 33.3 (s, O−CIV(CH3)3), 30.2 (s, CaIV-CIV(CH3)3), 26.0 (s, O-CIV(CH3)3). Anal. Calcd for C52H61N2O5P2Y: C, 66.10; H, 6.51; N, 2.96. Found: C, 65.89; H, 6.42; N, 2.85. General Polymerization Procedure. In a glovebox, rac-lactide (288 mg, 2 mmol) was dissolved in THF (1.8 mL). A stock solution of initiator (0.2 mL, 0.02 M) was injected into the reaction mixture, such that the overall concentration of lactide was 1 M and that of initiator was 2 mM. Aliquots were taken from the reaction under a nitrogen atmosphere and quenched with hexane (1−2 mL), and the solvent was allowed to evaporate. The crude product was analyzed by 1H NMR

spectroscopy and GPC. The conversion of LA to PLA was determined by integration of the methine proton peaks of the 1H NMR spectra” δ 5.00−5.30. The Ps value was determined by integration of the methine region of the homonuclear decoupled 1H NMR spectrum: δ 5.1− 5.24.12 The PLA number-averaged molecular weight, Mn, and polydispersity index (Mw/Mn; PDI) were determined using gel permeation chromatography equipped with multiangle laser light scattering (GPC-MALLS). The refractive angle increment for polylactide (dn/dc) in THF was 0.042 mL g−1.16 X-ray Crystallography. Data were collected at 150 K on a Bruker Kappa APEX II diffractometer using a Mo Kα (λ = 0.71069 Å) X-ray source and a graphite monochromator. The crystal structure was solved using SIR 9717 and Shelxl-97.18 ORTEP drawings were made using ORTEP III for Windows.17,19 X-ray crystallographic data for 1, 4, and 6 are given in Table 3.

Table 3. X-ray Crystallographic Data for Compounds 1, 4, and 6 1

4

6

formula

C66H87N2O4P2Y

C65H87N2O4P2Y

Mr space group T (°C) λ (Ǻ ) a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z d (g cm−3) μ (cm−1) R1a wR2b

1123.23 P21/m

1111.22 P21/c

C66H81N2O4P2Y, 2(C6H12) 1285.49 C2/c

−123 0.71069 10.652(1) 26.052(1) 11.446(1) 90.00 107.083(1) 90.00 3036.2(4) 2 1.229 1.061 0.0512 0.11277

−123 0.71069 11.409(1) 27.849(1) 21.019(1) 90.00 113.905(5) 90.00 6105.5(6) 4 1.209 1.054 0.0783 0.1588

−123 0.71069 35.816(1) 19.399(1) 25.180(1) 90.00 123.852(1) 90.00 14529.2(10) 8 1.175 0.895 0.0702 0.1679

a R1 =∑||F o | − |F c ||/∑|F o |. b wR2 ={∑[w(F o 2 − F c 2 ) 2 ]/ ∑[w(Fo2)2]}1/2; w−1 = σ2(Fo2) + (aP)2 + bP.

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ASSOCIATED CONTENT

S Supporting Information *

CIF files, tables, figures, and text giving crystallographic data for 1, 2, 4, and 6, additional experimental details, and characterization data. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (C.K.W.). Author Contributions §

These authors contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The CNRS, the Ecole Polytechnique, and the EPSRC (DTG studentship to C.B., EP/C544846/1 and EP/C544838/1) are acknowledged for funding this research. 1482

dx.doi.org/10.1021/om301129k | Organometallics 2013, 32, 1475−1483

Organometallics

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Article

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