Supporting Information for: Kinetic Analysis of the Immortal Ring-Opening Polymerization of Cyclic. Esters: A Case Study with Tin(II) Catalysts

Transcription

1 Supporting Information for: Kinetic Analysis of the Immortal Ring-Opening Polymerization of Cyclic Esters: A Case Study with Tin(II) Catalysts Lingfang Wang, Valentin Poirier, Fabio Ghiotto, Manfred Bochmann,*, Roderick D. Cannon,*, Jean-François Carpentier*, and Yann Sarazin*, Contents: Kinetic model for immortal ROP reactions Protocols for curve fitting to experimental data ROP Polymerization data Synthesis, Structure and Spectroscopic Data for Compound 7 Polymer analysis p. S2 p. S9 p. S13 p. S23 p. S28 S1

2 Kinetic model for immortal ROP reactions in the presence of excess alcohol. Derivation of eq (4). General aspects In immortal ROP of L-LA performed in the presence of an alcohol such as isopropanol, OHterminated macromonomers are produced, with [OH] remaining constant throughout the whole process. For our kinetic model we define the initiation of a catalyst (Cat) by the first insertion of monomer M into a metal alkoxide bond Cat-OR, characterised by the rate constant k i. Subsequent insertion steps are thought to proceed with the rate k p, and with identical k p assumed for all chain growth steps. These steps are summarised in eq 1(a) (c). Cat(OR) + M Cat(OMR), k i (1a) Cat(OMR) + M Cat(OM 2 R), k p (1b) Cat(OM 2 R) + M Cat(OM 3 R), k p (1c) etc. For convenience the concentrations may be abbreviated as [Cat(OR)] = x 0, [Cat(OMR)] = x 1, [Cat(OM 2 R)] = x 2, etc. Then the rate equations are dx 0 /dt = k i [M] x 0 dx 1 /dt = k p [M] x 1 + k i [M] x 0 dx 2 /dt = k p [M] x 2 + k p [M] x 1 dx 3 /dt = k p [M] x 3 + k p [M] x 2 (2a) (2b) (2c) (2d) etc. The alcohol is believed to react in additional steps such as S2

3 Cat(OM m R) + HOR HOM m R + Cat(OR), k e which generate a second family of polymers terminating in HO, but these too can react in the same way, so the general reaction is of the type Cat(OM m R) + HOM n R HOM m R + Cat(OM n R), k e known as interchange. We assume that all interchange reactions have the same rate constant k e except for those where the unpolymerized ROH enters, k e. Interchange with no depletion of monomer We can list the exchange reactions as follows: Cat(OR) + HOR Cat(OR) + HOR, k e (3.1a) Cat(OMR) + HOR Cat(OR) + HOMR, k e (3.1b) Cat(OM 2 R) + HOR Cat(OR) + HOM 2 R, k e (3.1c) Cat(OM m R) + HOR Cat(OR) + HOM m R, k e (3.1d) Cat(OR) + HOMR Cat(OMR) + HOR, k e (3.2a) Cat(OMR) + HOMR Cat(OMR) + HOMR, k e (3.2b) Cat(OM 2 R) + HOMR Cat(OMR) + HOM 2 R, k e (3.2c) S3

4 Cat(OM m R) + HOMR Cat(OMR) + HOM m R, k e (3.2d) Cat(OR) + HOM 2 R Cat(OM 2 R) + HOR, k e (3.3a) Cat(OMR) + HOM 2 R Cat(OM 2 R) + HOMR, k e (3.3b) Cat(OM 2 R) + HOM 2 R Cat(OM 2 R) + HOM 2 R, k e (3.3c) Cat(OM m R) + HOM 2 R Cat(OM 2 R) + HOM m R, k e (3.3d) and so on. Half of these reactions are the reverse of the other half, and reactions 3.1a, 3.2b, 3.3c etc are true exchanges with no net chemical reaction at all. Reactions 3.1 are the only ones which consume the free alcohol ROH, but reactions 3.2a, 3.3b etc regenerate the free alcohol. Reactions 3.1a, 3.2a, 3.3a consume the M-free catalyst Cat(OR) but 3.1b, 3.1c, 3.1d etc regenerate it. It is understood that reactions 3.1 etc can be expected to be faster than the ones in which longer chain alcohols react. In other words k e may larger than k e. But for the present we neglect this and write k e = k e, a simplification in agreement with Carother s theory of equal reactivity. As above, to save space the concentrations of molecules containing Sn are written [Cat(OR)] = x 0, [Cat(OMR)] = x 1, [Cat(OM 2 R)] = x 2, etc. Now we write the concentrations of molecules containing HO as [HOR] = y 0, [HOMR] = y 1, [HOM 2 R] = y 2, etc. Now we look at all the sets of reactions, 2, 3.1, 3.2, 3.3 etc. Considering the reactions in which [Cat(OR)] appears on either the left or right hand side we get S4

5 dx 0 /dt = k i [M] x 0 k e x 0 y 0 k e x 0 y 1 k e x 0 y k e x 0 y 0 + k e x 1 y 0 + k e x 2 y Summing all these terms we have dx 0 / dt = k i [M] x 0 k e x 0 Σ 0 y k e y 0 Σ 0 x = k i [M] x 0 k e x 0 [HO] T k e y 0 [Cat] T (3.4) Now we do the same with all the reactions which have HOR on either side. dy 0 / dt = k e x 0 y 0 k e x 1 y 0 k e x 2 y k e x 0 y 0 + k e x 0 y 1 + k e x 0 y = k e y 0 Σ 0 x n + k e x 0 Σ 0 y n = k e [HO] T x 0 k e [Cat] T y 0 (3.5) since Σ 0 x n is [Cat] T and Σ 0 y n is [HO] T This can be written as a pair of simultaneous linear homogeneous differential equations for x 0 and y 0 : dx 0 / dt = (k i [M] + k e [HO] T ) x 0 + k e [Cat] T y 0 (3.4) dy 0 / dt = k e [HO] T x 0 - k e [Cat] T y 0 (3.5) S5

6 The general solution for a set like this is well known (see e.g. S. Barnett, Matrix Methods for Engineers and Scientists (1979), eq. 6.96): x 0 = a x exp(λ 1 t) + b x exp(λ 2 t) + c x y 0 = a y exp(λ 1 t) + b y exp(λ 2 t) + c y (3.6a) (3.6b) where λ 1 and λ 2 are the eigenvalues of the matrix of the four coefficients in equations 3.4 and 3.5, and the a s, b s and c s are constants. These can be found by calculating the eigenvectors as described by Barrett, pp , but it easier to note what happens at the boundary conditions, i.e. when t = 0 and, then by substituting 3.6a and 3.6b into 3.4 and 3.5 and equating the coefficients of exp(λ 1 t) and exp(λ 2 t), we eventually get. The final results are x 0 = [(l + 1 ) 2 exp ( 1 t) - (l + 2 ) 1 exp ( 2 t)] / [k e ( 2-1 )] (3.7a) y 0 = [ 2 exp ( 1 t) - 1 exp ( 2 t)] [OH] T / ( 2-1 ) (3.7b) where 1 and 2 are given by 1,2 = (1/2) { - ( h + i + l ) ± [(h + i + l ) 2 4 i l ]} (3.8) and i = k i [M], h = k e [OH] T, l = k e [Cat] T. Notice that ( ) = - ( h + i + l ) and 1 2 = i l. S6

7 The Conversion The aim is to know the progress of the polymerization with time. We defined [M] B, the total concentration of bound monomer, [M] Bx, the concentration of monomer bound in molecules terminating with C, and [M] By, the concentration of monomer bound in molecules terminating with HO. Thus [M] Bx = Σ 0 n x n [M] By = Σ 0 n y n [M] B = [M] Bx + [M] By We look at all the sets of reactions, 2, 3.1, 3.2, 3.3 etc. Considering the reactions in which Cat(OR) appears on either the left or right hand side we get dx 0 /dt = k i [M] x 0 k e x 0 y 0 k e x 0 y 1 k e x 0 y 2 + k e x 0 y 0 + k e x 1 y 0 + k e x 2 y Summing all these terms we have dx 0 / dt = k i [M] x 0 k e x 0 Σ 0 y n k e y 0 Σ 0 x n = k i [M] x 0 k e x 0 [HO] T k e y 0 [Cat] T (4.1a) Next considering the reactions in which Cat(OMR) appears on either side we get dx 1 / dt = k p [M] x 1 k e x 1 [HO] T + k i [M] x 0 + k e y 1 [Cat] T (4.1b) S7

8 and in the same way for reactions in which Cat(OM 2 R) appears dx 2 / dt = k p [M] x 2 k e x 2 [HO] T + k p [M] x 1 + k e y 2 [Cat] T (4.1c) and similarly dx 3 / dt = k p [M] x 3 k e x 3 [HO] T + k p [M] x 2 + k e y 3 [Cat] T (4.1d) etc. Now we multiply equation 4.1a by zero, equation 4.1b by 1, equation 4.1c by 2, etc and add. This gives (d/dt) Σ 0 n x n = k p [HO] T Σ 0 n x n + (k i k p ) [M] x 0 + k p [M] [Cat] T + k e [Cat] T Σ 0 n y n (4.3) We now proceed in the same way with the rate expressions for the HO-terminated polymers dy 0 / dt = k e x 0 y 0 k e x 1 y 0 k e x 2 y k e x 0 y 0 + k e x 0 y 1 + k e x 0 y = k e [HO] T x 0 k e [Cat] T y 0 (4.4a) and similarly dy 1 / dt = k e [HO] T x 1 k e [Cat] T y 1 dy 2 / dt = k e [HO] T x 2 k e [Cat] T y 2 (4.4b) (4.4c) etc, and after multiplying the equations by 0, 1, 2 etc as before and adding, we get (d/dt) Σ 0 n y n = k e [Cat] T Σ 0 n y n + k e [HO] T Σ 0 n x n (4.5) hence S8

9 (d/dt) [M] B = (d/dt) Σ 0 n x n + (d/dt) Σ 0 n y n = (k i k p ) [M] x 0 + k p [M] [Cat] T (4.6) where x 0 is given by equation 3.7a, above; and on integrating from t = 0 to infinity [M] B = k p [M] [Cat] T t + (k i k p ) k e 1 [M] ( 2 1 ) 1 {(l + 1 ) [ 1 + exp( 1 t)] (l + 2 ) [ 1 + exp( 2 t)] } (4.7) Equation (4.7) above corresponds to eq(4) in the manuscript. Protocols for curve fitting to experimental data The equation 4 of the manuscript (aka equation 4.7 shown above) was applied, with λ 1,2 as defined in equation 3.4 of the manuscript (aka equation 3.8 of the Supporting Information, see above): λ 1,2 = ½{ (k e [OH] T + k i [M] + k e [Cat] T ) ± [(k e [OH] T + k i [M] + k e [Cat] T ) 2 4 k i [M] k e [Cat] T ] 1/2 } Substituted λ 1,2 afforded the expression of [M] B (mol L 1 ) vs. time (s) as a single equation. Curve fitting was carried out using Datafit software with the following expression: kp*[m]*[cat] T *t+(ki kp)*[m]*((ke*[cat] T +0.5*( (ke*[oh] T +ki*[m]+ke*[cat] T )+(( ke*[oh] T +ki*[m]+ke*[cat] T )^2 4*ki*[M]*ke*[Cat] T )^0.5))*0.5*( (ke*[oh] T +ki*[m]+ke* [Cat] T ) ((ke*[oh] T +ki*[m]+ke*[cat] T )^2 4*ki*[M]*ke*[Cat] T )^0.5)*(exp(0.5*( (ke*[oh] T+ki*[M]+ke*[Cat] T )+((ke*[oh] T +ki*[m]+ke*[cat] T )^2 4*ki*[M]*ke*[Cat] T )^0.5)*t) 1)/( 0.5*( (ke*[oh] T +ki*[m]+ke*[cat] T )+((ke*[oh] T +ki*[m]+ke*[cat] T )^2 4*ki*[M]*ke*[Cat ] T )^0.5)) (ke*[cat] T +0.5*( (ke*[oh] T +ki*[m]+ke*[cat] T ) ((ke*[oh] T +ki*[m]+ke*[cat] T ) ^2 4*ki*[M]*ke*[Cat] T )^0.5))*0.5*( (ke*[oh] T +ki*[m]+ke*[cat] T )+((ke*[oh] T +ki*[m]+ S9

10 ke*[cat] T )^2 4*ki*[M]*ke*[Cat] T )^0.5)*(exp(0.5*( (ke*[oh] T +ki*[m]+ke*[cat] T ) ((ke*[ OH] T +ki*[m]+ke*[cat] T )^2 4*ki*[M]*ke*[Cat] T )^0.5)*t) 1)/(0.5*( (ke*[oh] T +ki*[m]+ke *[Cat] T ) ((ke*[oh] T +ki*[m]+ke*[cat] T )^2 4*ki*[M]*ke*[Cat] T )^0.5)))/ke/(0.5*( (ke*[oh ] T +ki*[m]+ke*[cat] T ) ((ke*[oh] T +ki*[m]+ke*[cat] T )^2 4*ki*[M]*ke*[Cat] T )^0.5) 0.5*( (ke*[oh] T +ki*[m]+ke*[cat] T )+((ke*[oh] T +ki*[m]+ke*[cat] T )^2 4*ki*[M]*ke*[Cat] T )^0.5)) Non-linear regressions were performed with the software DataFit 9.0 (shareware). The concentration of enchained monomer [M] B was calculated according to [M] B = [M] T conversion, using data points collected for conversion typically below 35%, except for some experiments displayed at 60 o C to 40 45% conversions. All curve fittings were performed using a fixed value of k e set at 100 L mol 1 s 1. A time correction variable was introduced during the processing of curve-fitting experiments to stand for the time interval required by the reaction mixture in the NMR tube to reach temperature equilibration once inside the probe of the NMR spectrometer. Monomer equilibrium concentration The monomer equilibrium concentration has been omitted in the kinetic analysis. For lactide, it is about M at 25 C, M at 45 C and M at 60 C according to ln([m] eq ) = H /RT S /R, using H = 22.9 kj.mol 1 and S = 41.1 J.mol 1.K 1, as determined by Duda and Penczek. 1 The equilibrium concentration in toluene might be lower than those calculated by these authors (they used dioxane), but they could remain significant since our experiments were carried out at relatively low monomer concentration: [lactide] T = 0.33 M at 25 C, 0.5 M at 45 C and 0.5 M at 60 C. At these temperatures, maximum conversion would therefore S10

11 be 95.8, 95.1 and 92.9 %. The resulting asymptote at high conversion can be corrected in our model by substituting [M] B by [M] B [M] eq in eq (5) of the manuscript in the way reported by Duchateau and co-workers, 2 leading to: [M] B [M] eq = ([M] 0 [M] eq ) (1 e kp [Cat] T t ) (i) Taking lactide equilibrium concentration (eq (i) above) into consideration induces only minor modifications in the values of k p calculated in comparison with those found using eq (5) of the manuscript. Except in one case, we note however that these modifications tend to give values of k p somewhat closer to those determined with the model for the initial part of the polymerization (eq (4)). See Table S1 below for details. S11

12 Table S1. Values of k d in the ROP of L-lactide catalyzed by tin(ii)/iproh catalysts determined using equation 4 (manuscript) for the initial stage of the reaction, and equation 5 (manuscript) and equation (i) above for the monomer depletion phase. a Entry Sn T ( C) [M]/[Sn] T /[iproh] T [Sn] T (mm) k p 10 2 (L mol 1 s 1 ) Eq (4) a Eq (5) b Eq (i) c :1: ± ± ± :1: ± ± ± :1: ± ± ± :1: ± ± ± :1: ± ± ± :1: ± ± ± :1: ± ± ± :1: ± ± ± :1: ± ± ± :1: ± ± ± :1: ± ± ± :1: ± ± ± :1: ± ± ± 0.05 a Polymerizations in toluene-d 8 ; see experimental section for details. b Equation (4) from the manuscript. c Equation (5) from the manuscript. d Equation (i) given in the Supporting information. S12

13 Ln(kapp/T) Ln ([L-lactide]0/[L-lactide]t) Data on ROP Reactions C 70 C 60 C 50 C 40 C Time (s) /T (K-1) Figure S1. Semi-logarithmic plots of conversion vs. time (top) and corresponding Eyring analysis (bottom) for the immortal ROP of L-lactide with 1/iPrOH ([L-LA] T /[1] T /[iproh] T = 100:1:10, [L-LA] T = 1.0 M in toluene-d 8 ) in the temperature range C. The solid lines are the best linear fits. S13

14 Figure S2. Plot of k obs vs. [Sn] T for the polymerization of L-lactide catalyzed by {LO 2 }Sn(tBu (R)-lactate) (2) in the absence of added alcohol. Reaction conditions: T = 60 C, [L-LA] 0 = 1.0 M, [Sn] T = mm. k p = 4.84 ± L mol 1 s 1. Note that the intersection with the concentration axis was very close to zero, suggesting that minimal catalyst deactivation occurred through the presence of impurities. Table S2. Immortal ROP of L-lactide catalyzed by 1 5/iPrOH. a Entry Precat. [L-LA] T /[Sn] T /[iproh] T [L-LA] T (mol L 1 ) t (h) Yield b (%) M n,theo c (g mol 1 ) M n,sec d (g mol 1 ) M w /M n d 1 1 1,000:1: ,500 11, ,000:1:9 e, f ,100 16, :1:4 g ,100 11, :1:9 e ,300 6, :1:8 e ,800 6, ,000:1: ,700 12, ,000:1: ,200 12, a Polymerizations in toluene at 60 C, using mmol of L-lactide, mol of iproh and mol of tin(ii) precatalyst. b Isolated polymer yield. c Calculated according to [L-LA] T /[iproh] T monomer conversion d Determined by size exclusion chromatography vs. polystyrene standards and corrected by a factor of e Number of growing chains per Sn(II) atom = 10. f Alcohol = tbu lactate. 2 g Number of growing chains per tin(ii) atom = 5. S14

15 Figure S3. Monomer conversion vs. time (left) and semi-logarithmic plots of monomer conversion vs. time (right) for L-LA polymerization catalyzed by {LO 1 }Sn(N(SiMe 3 ) 2 ) (1) and iproh. Reaction in toluene-d 8, 25 C, [L-LA] T /[Sn] T /[iproh] T = 50:1:5, [Sn] T = 6.60 mm, [L-LA] T = 0.33 M, [iproh] T = 33.0 mm. Figure S4. Curve fitting of [L-LA] B vs. time for the immortal ROP of L-LA catalyzed by {LO 1 }Sn(N(SiMe 3 ) 2 ) (1) and iproh. Reaction in toluene-d 8, 25 C, [L-LA] T /[Sn] T /[iproh] T = 50:1:5, [Sn] T = 6.60 mm, [L-LA] T = 0.33 M, [iproh] T = 33.0 mm. Fitted curve: plain line; experimental data, black dots; k i = 0.66 ± L mol 1 s 1, k p = 1.05 ± L mol 1 s 1 ; R 2 > S15

16 Figure S5. Monomer conversion vs. time (left) and semi-logarithmic plots of monomer conversion vs. time (right) for L-LA polymerization catalyzed by {LO 1 }Sn(N(SiMe 3 ) 2 ) (1) and iproh. Reaction in toluene-d 8, 25 C, [L-LA] T /[Sn] T /[iproh] T = 66:1:5, [Sn] T = 5.00 mm, [L-LA] T = 0.33 M, [iproh] T = 25.0 mm. (entry 1 of Table 1) Figure S6. Curve fitting of [L-LA] B vs. time for the immortal ROP of L-LA catalyzed by {LO 1 }Sn(N(SiMe 3 ) 2 ) (1) and iproh. Reaction in toluene-d 8, 25 C, [L-LA] T /[Sn] T /[iproh] T = 66:1:5, [Sn] T = 5.00 mm, [L-LA] T = 0.33 M, [iproh] T = 25.0 mm. Fitted curve: plain line; experimental data, black dots; k i = 0.62 ± L mol 1 s 1, k p = 1.54 ± L mol 1 s 1 ; R 2 > (entry 1 of Table 1) S16

17 Figure S7. Monomer conversion vs. time (left) and semi-logarithmic plots of monomer conversion vs. time (right) for L-LA polymerization catalyzed by {LO 1 }Sn(N(SiMe 3 ) 2 ) (1) and iproh. Reaction in toluene-d 8, 25 C, [L-LA] T /[Sn] T /[iproh] T = 66:1:10; [L-LA] T = 0.33 M, [Sn] T = 5.00 mm, [iproh] T = 50 mm (entry 2 of Table 1) Figure S8. Curve fitting of [L-LA] B vs. time for the immortal ROP of L-LA catalyzed by {LO 1 }Sn(N(SiMe 3 ) 2 ) (1) and iproh. Reaction in toluene-d 8, 25 C, [L-LA] T /[Sn] T /[iproh] T = 66:1:10; [L-LA] T = 0.33 M, [Sn] T = 5.00 mm, [iproh] T = 50 mm. Fitted curve: plain line; experimental data, black dots; k i = 1.00 ± L mol 1 s 1, k p = 1.62 ± L mol 1 s 1 ; R 2 > (entry 2 of Table 1) S17

18 Figure S9. Curve fitting of [L-LA] B vs. time for the immortal ROP of L-LA catalyzed by Sn(N(SiMe 3 ) 2 ) 2 (5) and iproh. Reaction in toluene-d 8, 45 C, [L-LA] T /[Sn] T /[iproh] T = 100:1:10; [L-LA] T = 0.50 M, [Sn] T = 5.00 mm, [iproh] T = 50 mm. Fitted curve: plain line; experimental data, black dots; k i = ± L mol 1 s 1, k p = ± L mol 1 s 1 ; R 2 > (entry 5 of Table 1) S18

19 Figure S10. Top: Monomer conversion vs. time (left) and semi-logarithmic plots of monomer conversion vs. time (right) for L-LA polymerization catalyzed by {LO 2 }Sn(tBu(R)-lactate) (2) and iproh. Reaction in toluene-d 8, 60 C, [L-LA] T /[Sn] T /[iproh] T = 400:1:40; [L-LA] T = 1.00 M, [Sn] T = 2.50 mm, [iproh] T = 100 mm. Bottom : Curve fitting for this reaction. Fitted curve: plain line; experimental data, black dots; k i = ± L mol 1 s 1, k p = ± L mol 1 s 1 ; R 2 > (entry 12 of Table 1) S19

20 Figure S11. Top: Monomer conversion vs. time (left) and semi-logarithmic plots of monomer conversion vs. time (right) for TMC polymerization catalyzed by {LO 1 }Sn(N(SiMe 3 ) 2 ) (1) and iproh. Reaction in toluene-d 8, 60 C, [TMC] T /[Sn] T /[iproh] T = 100:1:10; [TMC] T = 1.00 M, [Sn] T = 10.0 mm, [iproh] T = 100 mm (entry 14 of Table 1). Bottom: Curve fitting. Fitted curve: plain line; experimental data, black dots; k i = 1.70 ± L mol 1 s 1, k p = 3.05 ± L mol 1 s 1 ; R 2 > (entry 14 of Table 1). S20

21 Figure S12. Top: Monomer conversion vs. time (left) and semi-logarithmic plots of monomer conversion vs. time (right) for L-LA polymerization catalyzed by {LO 1 }Ge(N(SiMe 3 ) 2 ) (6) and iproh. Reaction in toluene-d 8, 70 C, [L-LA] T /[Ge] T /[iproh] T = 200:1:20; [L-LA] T = 1.00 M, [Sn] T = 5.00 mm, [iproh] T = 100 mm. Bottom : Curve fitting for the germanium system. Fitted curve: plain line; experimental data, black dots; k i = 29.0 ± L mol 1 s 1, k p = 58.0 ± L mol 1 s 1 ; R 2 = S21

22 Table S3. ROP of L-lactide catalysed by the [Sn(OiPr) 2 ] 2 (3) at various [Sn]/[ROH] ratios. a Entry [L-LA] T /[3] T /[iproh] T [iproh] T b [macromolecules] T /[Sn] T (mm) 1 100/1/ /1/ /1/ /1/ /1/ /1/ a Conditions: toluene-d 8, 60 C, [L-LA] T = 1.0 M, [Sn] T = 10.0 mm. b [macromolecules] T = 2 [Sn] T + [iproh] T. k obs (s 1 ) S22

23 Synthesis, Structure and Spectroscopic Data for Compound 7. A solution of tin bis(isopropoxide) (0.15 g, 0.60 mmol) in pentane (10 ml) was added at 30 C over 30 min to a solution of Sn(N(SiMe 3 ) 2 ) 2 (0.28 g, 0.60 mmol) in pentane (20 ml). The mixture turned from deep orange to yellow. The solution was stirred for 90 min at 25 C, and the volatiles were removed in vacuo. The resulting solid was dried to give 6 as a yellow powder (0.37 g, 90%). Single-crystals for X-ray diffraction were grown by recrystallization from pentane. 1 H NMR (toluene-d 8, MHz, 25 C): δ = 4.32 (m, 1H, CH(CH 3 ) 2 ), 1.20 (d, 3 J HH = 6.0 Hz, 6H, CH(CH 3 ) 2 ), 0.39 (s, 18H, N(Si(CH 3 ) 3 ) 2 ) ppm. 13 C{ 1 H} NMR (toluened 8, MHz, 25 C): δ 68.13(CH(CH 3 ) 2 ), (CH(CH 3 ) 2 ), 7.11 (N(Si(CH 3 ) 3 ) 2 ) ppm. 29 Si{ 1 H} NMR (toluene-d 8, MHz, 60 C): δ Si = 1.30 (d, 2 J 29Si-119Sn = 15.3 Hz) ppm. 119 Sn{ 1 H} NMR (toluene-d 8, MHz, 60 C): δ Sn = ppm (t, 1 J 119Sn-14N = 263 Hz). Anal. Calc for C 9 H 25 NOSi 2 Sn ( g mol 1 ): C 31.96, H 7.45, N Found C 31.80, H 7.32, N X-ray diffraction. Crystals of [Sn( -OiPr)(N(SiMe 3 ) 2 ] 2 (7) suitable for X-ray diffraction analysis were obtained by recrystallization of the purified compound. Diffraction data were collected at 150(2) K using a Bruker APEX CCD diffractometer with graphitemonochromated MoK radiation ( = Å). A combination of and scans was carried out to obtain at least a unique data set. The crystal structures were solved by direct methods, remaining atoms were located from difference Fourier synthesis followed by fullmatrix least-squares refinement based on F2 (programs SIR97 and SHELXL-97). 3 Carbonand oxygen-bound hydrogen atoms were placed at calculated positions and forced to ride on the attached atom. All non-hydrogen atoms were refined with anisotropic displacement parameters. The locations of the largest peaks in the final difference Fourier map calculation as well as the magnitude of the residual electron densities were of no chemical significance. S23

24 Relevant collection and refinement data are summarized in Table S3. Crystal data, details of data collection and structure refinement for [Sn( -OiPr)(N(SiMe 3 ) 2 ] 2 (7) (CCDC ) can be obtained free of charge from the Cambridge Crystallographic Data Centre via Table S4. Summary of crystallographic data for [Sn( -OiPr)(N(SiMe 3 ) 2 ] 2 (7). [Sn( -OiPr)(N(SiMe 3 )] 2 Formula C 81 H 225 N 9 O 9 Si 18 Sn 9 CCDC n Formula weight Crystal system Triclinic Space group P -1 a(å) (8) b(å) (10) c(å) (3) α( o ) (4) β( o ) (4) γ( o ) (4) Volume (Å 3 ) (9) Z 2 Density(g/cm 3 ) Abs. coefficient (mm -1 ) F(000) 3096 Crystal size mm range ( o ) 2.95 to < h < 13 Limiting indices 20 < k < < l < 58 R(int) Reflections collected Reflections. unique [I>2 (I)] Data/restraints/param / 3 / 958 Completeness to max Goodness-of-fit R 1 [I>2 (I)] (all data) (0.2042) wr 2 [I>2 (I)] (all data) (0.2373) Largest diff. e A and S24

25 Figure S13. ORTEP diagram of the molecular structure of [Sn( -OiPr){N(SiMe 3 ) 2 }] 2 (7). Hydrogen atoms are omitted for clarity. Only one of the five independent molecules found in the asymmetric unit is depicted. Selected bond length (Å) and angles: Sn(7) N(7) = 2.126(11), Sn(7) O(7) = 2.168(12), Sn(7) O(8) = 2.196(8), Sn(8) N(8) = 2.132(10), Sn(8) O(8) = 2.169(11), Sn(8) O(7) = 2.182(9); N(7) Sn(7) O(7) = 95.9(4), N(7) Sn(7) O(8) = 102.6(4), O(7) Sn(7) O(8) = 72.7(4), N(8) Sn(8) O(8) = 96.4(4), N(8) Sn(8) O(7) = 100.9(4), O(8) Sn(8) O(7) = 73.0(4). S25

26 Figure S14. Diffusion-formula weight correlation analysis based on 1 H DOSY NMR (toluene-d 8, MHz, 298 K) for [Sn(μ-OiPr){N(SiMe 3 ) 2 }] 2 (7) The reference compounds (1,3-dioxolan-2-one, g mol 1 ; naphthalene, g mol 1 ; pyrene, g mol 1 ; tetra(trimethylsilane)silane, g mol 1 ; Sn(N(SiMe 3 ) 2 ) 2, g mol 1 ; {LO} 2 Sn, g mol 1 ) are shown (0.08 M solutions in toluene-d 8 ). Diffusion-formula weight (D-fw) correlation analysis 5 based on diffusion coefficient measurements in toluene-d 8 by 1 H DOSY NMR spectroscopy ( MHz) indicates that tin(amino)(isopropoxide) is essentially dimeric in toluene, i.e. found under the form [Sn(μ- OiPr){N(SiMe 3 ) 2 }] 2. The 1 H DOSY D fw plot, with a good R 2 correlation coefficient (0.9903), gives a predicted formula weight of g mol 1, i.e. less than 5.5% more than the theoretical value for the dimeric form [Sn(μ-OiPr){N(SiMe 3 ) 2 }] 2 (fw = g mol 1 ). S26

27 Figure S Sn{ 1 H} NMR spectra ( MHz, toluene-d 8, 60 C) for [Sn( - OiPr)(N(SiMe 3 ) 2 ] 2 (7), mixtures of [Sn(OiPr) 2 ] 2 (3) and Sn(N(SiMe 3 ) 2 ) 2 (5), and mixtures of iproh and Sn(N(SiMe 3 ) 2 ) 2.. S27

28 Figure S16. MALDI-ToF MS (main population: Na + ) of a PLLA sample produced by [Sn(μ- OiPr)(N(SiMe 3 ) 2 ] 2 (7). Observed molecular weights for the on-matrix compounds and those calculated using the (CH 3 ) 2 CHO(C 6 H 8 O 4 ) x H Na + formula, where x represents the degree of polymerization differ by less than 0.5Da. Polymerization conditions: [L-LA] T /[7] T = 25:1, [L- LA] T = 0.75 M, toluene, 60 C, 4 h, yield = 84%. SEC analysis: M n = 5,300 g mol 1, M w /M n = S28

29 Figure S17. 1 H NMR spectrum of a PLLA sample produced by [Sn(μ-OiPr)(N(SiMe 3 ) 2 ] 2 (7) (CDCl 3, 500 MHz, 25 o C). Polymerization conditions: [L-LA] T /[7] T = 25:1, [L-LA] T = 0.75 M, toluene, 60 C, 4 h, yield = 84%. SEC analysis: M n = 5,300 g mol 1, M w /M n = S29

30 Figure S C{ 1 H} NMR spectrum of a PLLA sample produced by [Sn(μ- OiPr)(N(SiMe 3 ) 2 ] 2 (7) (CDCl 3, 125 MHz, 25 o C). Polymerization conditions: [L-LA] T /[7] T = 25:1, [L-LA] T = 0.75 M, toluene, 60 C, 4 h, yield = 84%. SEC analysis: M n = 5,300 g mol 1, M w /M n = S30

31 References (1) Duda, A.; Penczek, S. Macromolecules 1990, 23, (b) Kowalski, A.; Duda, A.; Penczek, S. Macromol. Rapid Commun. 1998, 19, 567. (2) Pepels, M. P. F.; Bouyahyi, M.; Heise, A.; Duchateau, R. Macromolecules 2013, 46, (3) (a) Sheldrick, G. M. SHELXS-97, Program for the Determination of Crystal Structures; University of Goettingen: Germany, (b) Sheldrick, G. M. SHELXL- 97, Program for the Refinement of Crystal Structures; University of Goettingen: Germany, (4) Wang, L.; Bochmann, M.; Cannon, R. D.; Carpentier, J.-F.; Roisnel, T.; Sarazin, Y. Eur. J. Inorg. Chem, 2013, (5) (a) Li, D.; Keresztes, I.; Hopson, R.; Williard, P. G. Acc. Chem. Res. 2009, 42, 270. (b) Kagan, G.; Li, W.; Li, D.; Hopson, R.; Williard, P. G. J. Am. Chem. Soc. 2011, 133, S31