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Article

Tin Complexes Derived from the Acids Ph2C(X)CO2H (X = OH, NH2): Structure and ROP Capability

by
Timothy J. Prior
and
Carl Redshaw
*
Plastics Collaboratory, Chemistry, School of Natural Sciences, University of Hull, Cottingham Road, Hull HU6 7RX, UK
*
Author to whom correspondence should be addressed.
Catalysts 2025, 15(3), 261; https://doi.org/10.3390/catal15030261
Submission received: 29 January 2025 / Revised: 25 February 2025 / Accepted: 7 March 2025 / Published: 9 March 2025
(This article belongs to the Special Issue State-of-the-Art Polymerization Catalysis)
Browse Figures
Versions Notes

Abstract

:
Interaction of [Sn(OtBu)4] with the acid 2,2′-diphenylgylcine, Ph2C(X)CO2H (X = NH2), affords the complex {Sn[Ph2C(NH2)(CO2)]4}·2MeCN (1·2MeCN) after work-up, whereas when X = OH (benzilic acid), the complex {Sn[Ph2C(O)(CO2)]2(CH3CO2H)2} (2) is isolated. In 1·2MeCN, the four 2,2′-diphenylglycinate ligands adopt three different coordination modes (two N,O-chelates, an O,O-chelate, and a monodentate carboxylate ligand), whilst in 2, two cis-O,O-chelate ligands are present along with two acetic acid ligands, the latter being derived from hydrolysis of acetonitrile. Both 1 and 2 have been screened as catalysts for the ring opening polymerization of ε-caprolactone and δ-valerolactone; for comparison, the commercial catalyst [Sn(Oct)2], where Oct = 2-ethylhexanoate, and the precursor [Sn(OtBu)4] have been screened under similar conditions. The products were of low to high molecular weight for PCL and low to moderate molecular weight for PVL, with wide Ð values, and they comprised several types of polymer families, including OH-terminated, OH/OMe-terminated, and cyclic polymers. For both monomers, kinetic profiles indicated that [Sn(Oct)2] outperformed 1, 2, and [Sn(OtBu)4], though under certain conditions, 1 and 2 afforded high-molecular weight products with better control.

Graphical Abstract

1. Introduction

Petroleum-based plastics continue to be essential for a variety of everyday applications; however, the issues associated with global plastic pollution are driving the search for more environmentally friendly materials [1,2,3]. With this in mind, much research has focused on the ring opening polymerization (ROP) of cyclic esters. This process typically employs a catalyst, which can be either metal- or organic-based [4,5,6,7,8,9,10,11,12], and in the former case, the active species tends to be either a metal alkoxide or carboxylate. The other ancillary ligands bound to the catalytic metal centre also play a crucial role in controlling the local sterics and electronics of the system and can also greatly influence other properties such as solubility. Commercially, the catalyst of choice is tin octanoate, [Sn(Oct)2], which was selected given its high catalytic activity (high reaction and conversion rates), ability to afford high-molecular weight products, and relatively low cost, despite the cytotoxicity associated with tin compounds [13]. There is considerable interest in the development of new tin-based catalysts for the ROP of cyclic esters [14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36]. For example, Limwanich et al. have recently investigated the microwave-assisted ROP of ε-caprolactone under solvent-free conditions using n-butyltin(IV) chlorides [36]. We have been investigating the coordination chemistry of the acids Ph2C(X)CO2H, where X = NH2 or OH [37,38,39,40,41,42,43,44,45], given their ability to impart high crystallinity on subsequent products [46]. Given this, we have extended our studies of these acids to tin chemistry and report herein two products arising from the interaction of Ph2C(X)CO2H, X = NH2, OH, with [Sn(OtBu)4], Chart 1. [Sn(OtBu)4] was chosen as the entry point, despite the increased toxicity associated with Sn(IV), as solid Sn(II) alkoxides tend to suffer from solubility issues [32]. The tin products 1 and 2 have been screened for their ROP capability with the cyclic esters ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL). Results are compared against the commercial catalyst [Sn(Oct)2], where Oct = 2-ethylhexanoate, and the precursor [Sn(OtBu)4], which have been screened under the same conditions.

2. Results and Discussion

2.1. Diphenylglycine

Reaction of [Sn(OtBu)4] with Ph2C(NH2)(CO2H), dpgH, in refluxing toluene afforded the complex {Sn[Ph2C(NH2)(CO2)]4}∙2MeCN (1∙2MeCN) after work-up (extraction into MeCN). Single crystals suitable for X-ray diffraction were grown from a saturated MeCN solution on standing for 48h at 0 °C. The molecular structure is shown in Figure 1, with selected bond lengths and angles given in the caption; an alternative view of 1∙2MeCN is given in the Supplementary Materials (Figure S1). The complex crystallises in the centrosymmetric space group P1 with a single, discrete tin complex in the asymmetric unit. The central Sn(VI) ion is seven-coordinate; four dpg− anions are bound at the tin centre, but there are three different coordination modes. The first two dpg anions form five-membered chelates through the carboxylate and amine group (O1, N1 and O3, N2). This can be classified using the Harris notation [47] as a [1.011] binding mode. The third ligand binds through a chelating carboxylate (atoms O5 and O6) in mode [1.110]. The final ligand binds through a single oxygen of the carboxylate (O7). The different coordination modes are readily apparent from the carboxylate bond lengths. The assignment was greatly aided by excellent-quality difference Fourier maps which allowed for H-atoms to be identified. Hydrogens attached to carbon were fitted with a riding model; those attached to nitrogen were refined freely, subject to restraints that all N-H distances be the same with a standard deviation of 0.03 Å, and bond angles were similarly restrained. For the five-membered chelates, the C-O bond lengths are 1.308(3) and 1.216(3) Å for C1 and 1.298(3) and 1.216(3) Å for C15. The chelating carboxylate centred on C29 has C-O bond lengths of 1.282(3) and 1.245(3) Å. The strictly monodentate carboxylate centred on C43 has C-O bond lengths of 1.302(3) and 1.220(3) Å. There is very minor disorder in the position of one of the phenyl groups (two orientations in the ratio 0.569:0.431(15)), but this was modelled conservatively using standard techniques, involving bond length restraints for equivalent atoms in different disorder components. In addition to the tin complex, the asymmetric unit contains two well-resolved molecules of acetonitrile which act as hydrogen bond acceptors to two NH2 groups of the complex, forming a D 1 1 ( 2 ) hydrogen-bonding motif [48]. The phenyl rings are orientated in a propellor-like fashion, as noted for a number of benzilate complexes [49].
There are no intramolecular hydrogen bonds. There is extensive N-H∙∙∙N hydrogen bonding between adjacent molecules, but surprisingly, there are no N-H∙∙∙O interactions. Most notably, adjacent molecules related by the inversion centre form an R 2 2 14 embrace through N-H∙∙∙N hydrogen bonds. There is also evidence for C-H∙∙∙O interactions between adjacent molecules.

2.2. Benzilic Acid

Similar use of benzilic acid led to the complex {Sn[Ph2C(O)(CO2)]2(CH3CO2H)2} after work-up (MeCN) (2). Single crystals suitable for X-ray diffraction were grown from a saturated MeCN solution, standing for 48h at 0 °C. The molecular structure is shown in Figure 2, with selected bond lengths and angles given in the caption; an alternative view of 2 is given in the Supplementary Materials (Figure S2). The complex crystallises in the non-centric space group I-42d, with one half a complex in the asymmetric unit. There is minor disorder in the position of one of the phenyl groups (two orientations in the ratio 0.55:0.45(5)), but this was modelled conservatively using standard techniques, involving bond length restraints for equivalent atoms in different disorder components. Each Sn is six coordinate, and two doubly-deprotonated benzilic acid ligands form five-membered chelates to the Sn in a cis fashion. The remaining two coordination sites are completed by the carbonyl oxygen of acetic acid (C=O distance for the binding oxygen is 1.26(2) Å and for the C-OH, the C-O distance is 1.34(2) Å). The O-H group is not deprotonated but forms an intramolecular hydrogen bond to the carbonyl of the benzilic acid with motif S 1 1 ( 6 ) . The crystal as a whole was found to contain a single enantiomer (Flack parameter 0.05(3)). The acetic acid ligand is thought to arise via the hydrolysis of MeCN; such a process usually occurs in the presence of an acid or base [50,51,52].
There is no included solvent in the structure despite the fact that four pockets of approximately 3.6% of the cell volume are present.
1H NMR spectra for 1 and 2 are provided in the Supplementary Materials (Figures S3 and S4).

3. Ring Opening Polymerization (ROP)

3.1. Ring Opening Polymerization of ε-Caprolactone (ε-CL)

Complexes 1 and 2 have been screened for their ability to act as catalysts for the ROP of ε-caprolactone (ε-CL), and the results are presented in Table 1. Results for 1 and 2 are compared with the industrially employed catalyst Sn(Oct)2. For 1, the ratio of [ε-CL]:[Sn] was varied between 100:1 and 1000:1 at 130 °C over 24 h under N2 or air. Complexes 1 and 2 were found to be active under these polymerization conditions with similar monomer conversions (≥90%, except for entry 4 at 81%), affording polymers with moderate to relatively high molecular weights, with 1 under N2 (entry 3, Table 1) affording the highest at ca. 48,750 Da, albeit with poor control (Ð = 3.81); selected GPC traces are given in the Supplementary Materials (Figures S5–S11). Interestingly, consistent with the wide Ð values, the MALDI-TOF spectra revealed several families of products, including OH-terminated polymers and cyclic polymers (e.g., Figure 3, Figure 4, Figure 5 and Figure 6). There was evidence of transesterification, and all observed Mn values were significantly lower than the calculated values. The polymers obtained using [Sn(Oct)2] consistently gave higher molecular weights than those obtained using 1 and 2 under the same conditions. MALDI-ToF spectra for the PCL obtained via the use of [Sn(Oct)2] revealed the products to be mostly linear polymers with H/OH end groups (e.g., see Figure 6). At ambient temperature (15 °C), all complexes exhibited little or no activity.
A kinetic study (Figure 7) conducted using 500:1 ([ε-CL]:[cat]) at 110 °C revealed the rate trend [Sn(Oct)2] > 1 > 2 > [Sn(OtBu)4]. Both [Sn(Oct)2] and 1 are rather sluggish over the first 15 h (about 25 h for Sn(OtBu)4), consistent with a structural change under these conditions to a more active species. For the individual kinetic traces, see Figures S12–S15 in the Supplementary Materials.
We note that during metal-free studies, we observed that benzilic acid was active for the ROP of ε-CL with near quantitative conversions when using high-catalyst loadings (20:1) at 150 °C over 24 h, whereas for diphenylglycine, conversions were ≤5% at 150 °C over 24 h, with or without BnOH present [41].

3.2. Ring Opening Polymerization of δ-Valerolactone (δ-VL)

Based on the ε-CL results, the complexes were screened for the ROP of δ-VL using the ratio of [VL]:[catalyst] of 500:1 (Table 2). All complexes were found to be active under these polymerization conditions with monomer conversions (≥77%), affording relatively low to moderate-molecular weight polymers; selected GPC traces are given in the Supplementary Materials (Figures S16–S23). Even at ambient temperature, 1, 2, Sn(Oct)2, and [Sn(OtBu)4] were capable of the ROP of δ-VL with good conversions. This behaviour contrasts with previous ROP studies, where more robust conditions are usually needed for the ROP of δ-VL versus ε-Cl [38,39], and it is inconsistent with the thermodynamic parameters for these lactones [55].
1H NMR and mass spectra of the PVL again indicated that the products contained both linear and cyclic species. The MALDI-TOF spectra revealed several families of products, including H/OH- and H/OMe-terminated polymers and cyclic polymers (e.g., Figure 8, Figure 9 and Figure 10; expansions are given as inserts). As for PCL, there was evidence of transesterification, and all observed PVL Mn values were significantly lower than the calculated values.
A kinetic study (Figure 11) conducted using 500:1 ([ε-CL]:[cat]) at 110 °C revealed the rate trend [Sn(Oct)2] > 1 > [Sn(OtBu)4] > 2. In this case, sluggish behaviour is only observed for 1 over about 12 h and, as in the case of ε-CL, for Sn(OtBu)4 over about 25 h. For the individual kinetic traces, see Figures S24–S27 in the Supplementary Materials.

4. TGA Measurements

The stability of the complexes at the polymerization temperature was checked by TGA. The runs indicated that both systems were stable, and in the case of 1∙2MeCN, only solvent of crystallization (MeCN) was lost (with calc./obsv. values of ~7%) (see Figure 12).

5. Materials and Methods

All manipulations were carried out under an atmosphere of nitrogen using standard Schlenk line and cannula techniques or a conventional N2-filled glove box. Solvents were refluxed over the appropriate drying agents and distilled and degassed prior to use, i.e., toluene was refluxed over Na; acetonitrile was refluxed over calcium hydride. These were purchased from commercial sources and used directly. ε-Caprolactone (Fisher Scientific, Loughborough, UK) and δ-valerolactone (Sigma Aldrich, Gillingham, UK) were dried over CaH2 and then distilled. Tin tert-butoxide (Sigma Aldrich, UK) was stored under nitrogen in a dry box. 2,2′-diphenylglycine (Sigma Aldrich, UK) and benzilic acid (Sigma Aldrich, UK) were dried under vacuum at 80 °C for 4 h prior to use. Elemental analyses were performed at the London Metropolitan University or Xi’an Rare Metal Materials Research Institute Co., Ltd. (Xi’an, China). FTIR spectra (nujol mulls, KBr windows) were recorded on a Nicolet Avatar 360 FT-IR spectrometer. 1H NMR spectra were recorded at 400.2 MHz on a JEOL ECZ 400S spectrometer (Peabody, MA, USA), with TMS δH = 0 as the internal standard or residual protic solvent; chemical shifts are given in ppm (δ). Matrix-Assisted Laser Desorption/Ionization–Time of Flight (MALDI-TOF) mass spectrometry was performed on a Bruker III smart beam in linear mode. MALDI-TOF mass spectra were acquired by averaging at least 100 laser shots. Molecular weights were calculated from the experimental traces using the OmniSEC software (Malvern Panalytical Ltd., Malvern, UK, v11.35). For the TGA runs, data were collected on a PerkinElmer TGA 400 (Shelton, CT, USA) using PyrisTM software (v11.0) and a rate of 10 °C per min over the 30 °C to 800 °C under N2. Sample weights were typically between 3 and 5 mg.

5.1. Synthesis of {Sn[Ph2C(NH2)(CO2)]4}∙2MeCN (1∙2MeCN)

Ph2C(NH2)CO2H (1.00 g, 4.40 mmol) and Sn(OtBu)4 (0.90 g (0.85 mL), 2.20 mmol) were refluxed in toluene (20 mL) for 12 h. On cooling, the volatiles were removed in vacuo, and the residue was extracted into warm MeCN (30 mL). Removal of the MeCN afforded a white solid. Yield: 1.02 g, 84% (based on dpgH). C56H48N4O8Sn∙2MeCN requires C 65.17, H 4.92, N 7.60%. Found C 65.26, H 4.89, N 7.71%. IR: 3406bw, 3185bw, 2357w, 2336w, 1958w, 1867w, 1659m, 1575s, 1489m, 1403s, 1318m, 1277m, 1261s, 1209w, 1169m, 1158m, 1094s, 1029s, 941w, 918w, 895m, 803s, 764m, 721m, 699s, 676w, 638m. M.S. 1023 (M+–2MeCN). 1H NMR (CDCl3) δ: 7.21 (bs, 40H, arylH), 3.45 (bs, 8H, NH2), 1.96 (s, 6H, MeCN).

5.2. Synthesis of {Sn[Ph2C(O)(CO2)]2(CH3CO2H)2} (2)

Ph2C(OH)CO2H (1.00 g, 4.38 mmol) and Sn(OtBu)4 (0.60 g, 1.46 mmol) were refluxed in toluene (20 mL) for 12 h. On cooling, the volatiles were removed in vacuo, and the residue was extracted into warm MeCN (30 mL). Removal of the MeCN afforded a white solid. Yield: 0.92 g, 91% (based on Sn). C32H28O10Sn requires C 55.60, H 4.08%. Found C 55.14, H 3.93%. IR: 1957w, 1881w, 1810w, 1650s, 1560s, 1300s, 1281s, 1210m, 1164s, 1085m, 1047s, 1029s, 1002m, 985m, 940w, 906m, 822m, 783m, 758m, 723s, 698m, 621w. M.S. 404 (M+—acetic acid—doubly deprotonated benzilic acid). 1H NMR (CDCl3) δ: 7.63 (dd, 1H, J 8.0 Hz, J’ 2.4 Hz, arylH), 7.51–7.41 (overlapping m, 7H, arylH), 7.33 (bm, 8H, arylH), 7.17 (bm, 2H, arylH), 7.05 (bm, 2H, arylH), 1.85 (bs, 2H, OH), 1.26 (s, 6H, Me).

5.3. ROP of ɛ-Caprolactone (ε-CL) and δ-Valerolactone (δ-VL)

The pre-catalyst (0.010 mmol) was added to a Schlenk tube in the glovebox at room temperature. For ROPs in solution, toluene (5 mL) was added. The appropriate amount of ε-CL (or δ-VL) was added, and the reaction mixture was then placed into a sand bath pre-heated at 130 °C and heated for the prescribed time (24 h) under either N2 or air. The polymerization mixture was quenched on addition of an excess of glacial acetic acid (0.2 mL) in methanol (50 mL). The resultant polymer was then collected on filter paper and dried in vacuo. GPC (in THF) were used to determine molecular weights (Mn and Ð) of the polymer products.

5.4. Kinetic Studies

The polymerizations were carried out at 110 °C in toluene (2 mL) using 0.010 mmol of complex. The molar ratio of monomer to initiator to co-catalyst was fixed at 500:1, and at appropriate time intervals, 0.5 μL aliquots were removed (under N2) and were quenched with wet CDCl3. The percent conversion of monomer to polymer was determined using 1H NMR spectroscopy.

5.5. X-Ray Crystallography

In both cases, crystals suitable for an X-ray diffraction study were grown from a saturated MeCN solution at 0 °C. Single crystal X-ray diffraction data were collected by the UK National Crystallography Service (NCS, Southampton, UK) using a Rigaku Oxford Diffraction diffractometer operating with a rotating anode X-ray generator and HyPix 6000HE detector (Neu-Isenberg, Germany). Table 3 contains basic crystallographic data and refinements details. It happens that one structure was collected using a Cu source and one with a Mo source; this normally reflects which instrument is available at the NCS at the time the sample is studied. There are not technical reasons for the different choice of sources. Samples were mounted on Mitegen loops and held at 100 K using an Oxford Cryosystems nitrogen gas cryostream. Both structures were solved and refined routinely [56,57,58]. H atoms were included in a riding model; Uiso(H) was set to 120% of that of the carrier atoms except for OH, NH3, and CH3 (150%). Further details are presented in Table 2. CCDC 2410598-9 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures (accessed on 10 January 2025).

6. Conclusions

In conclusion, the use of the acids Ph2C(X)CO2H on reaction with tin tert-butoxide afforded the complexes {Sn[Ph2C(NH2)(CO2)]4}·2MeCN (1·2MeCN) for X = NH2 or the complex {Sn[Ph2C(O)(CO2)]2(CH3CO2H)2} (2) for X = OH. These tin-based systems are active as catalysts for the ROP of ε-caprolactone and δ-valerolactone when employed in solution (toluene) or as melts under either air or N2. The products are of low to high molecular weight for PCL (1150–48,750 Da) and low to moderate molecular weight for PVL (1630–7720 Da), generally with broad Ð (1.48–3.81 for PCL; 1.29–3.24 for PVL). A number of families were evident in the MALDI-ToF mass spectra, with polymers present assigned to those terminated with H/OH, H/OMe, and cyclic polymers. Kinetic profiles indicated that [Sn(Oct)2] outperformed 1 and 2, though under certain conditions, 1 and 2 afforded high-molecular weight products with better control.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/catal15030261/s1, Figure S1. An alternative view of 1∙2MeCN. Figure S2. An alternative view of 2. Figures S3 and S4. 1H NMR spectra of 1∙2MeCN and 2. Figures S5–S11. Selected gpc traces for PCL. Figures S12–S15. Kinetic profiles for PCL formation using 1, 2, [Sn(Oct)2] and [Sn(OtBu)4]. Figures S16–S23. Selected gpc traces for PVL. Figures S24–S27. Kinetic profiles for PVL formation using 1, 2, [Sn(Oct)2] and [Sn(OtBu)4].

Author Contributions

T.J.P.: Investigation, writing—review and editing. C.R.: Conceptualization, writing—original draft, writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by UKRI Creative Circular Plastic grant (EP/S025537/1).

Data Availability Statement

Data are contained within the article and Supplementary Materials.

Acknowledgments

CR thanks the EPSRC for support (grant no. EP/S025537/1). The EPSRC National Crystallographic Service Centre at Southampton University is thanked for data collection of 1·2MeCN and 2.

Conflicts of Interest

There are no conflicts of interest to declare.

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Catalysts 15 00261 ch001
Chart 1. The acids Ph2C(X)CO2H (X = OH, NH2) and the complexes 1 and 2.
Chart 1. The acids Ph2C(X)CO2H (X = OH, NH2) and the complexes 1 and 2.
Catalysts 15 00261 ch001
Catalysts 15 00261 g001
Figure 1. View of molecular structure of {Sn[Ph2C(NH2)(CO2)]4}∙2MeCN (1∙2MeCN), drawn as 50% probability ellipsoids. For clarity, unbound solvent molecules have been omitted. Selected bond lengths (Å) and angles (°): Sn1—O1 2.0576(16), Sn1—O3 2.0923(18), Sn1—O5 2.1461(18), Sn1—O7 2.0687(16), Sn1—N1 2.2244(19), Sn—N2 2.2208(19); O1—Sn—N1 75.59(6), O3—Sn—N2 75.26(7), O5—Sn—O6 56.54(6), O1—Sn—O7 161.00(7).
Figure 1. View of molecular structure of {Sn[Ph2C(NH2)(CO2)]4}∙2MeCN (1∙2MeCN), drawn as 50% probability ellipsoids. For clarity, unbound solvent molecules have been omitted. Selected bond lengths (Å) and angles (°): Sn1—O1 2.0576(16), Sn1—O3 2.0923(18), Sn1—O5 2.1461(18), Sn1—O7 2.0687(16), Sn1—N1 2.2244(19), Sn—N2 2.2208(19); O1—Sn—N1 75.59(6), O3—Sn—N2 75.26(7), O5—Sn—O6 56.54(6), O1—Sn—O7 161.00(7).
Catalysts 15 00261 g001
Catalysts 15 00261 g002
Figure 2. View of molecular structure of {Sn[Ph2C(O)(CO2)]2(CH3CO2H)2}, drawn as 30% probability ellipsoids. For clarity, minor disorder is not shown. Symmetry operation used to generate equivalent atoms: x, 1.5−y, 1.25−z. Selected bond lengths (Å) and angles (°): Sn1—O2 2.044(10), Sn1—O3 1.965(8), Sn1—O4 2.073(10); O2—Sn—O3 81.6(4), O2—Sn—O4 169.7(4).
Figure 2. View of molecular structure of {Sn[Ph2C(O)(CO2)]2(CH3CO2H)2}, drawn as 30% probability ellipsoids. For clarity, minor disorder is not shown. Symmetry operation used to generate equivalent atoms: x, 1.5−y, 1.25−z. Selected bond lengths (Å) and angles (°): Sn1—O2 2.044(10), Sn1—O3 1.965(8), Sn1—O4 2.073(10); O2—Sn—O3 81.6(4), O2—Sn—O4 169.7(4).
Catalysts 15 00261 g002
Catalysts 15 00261 g003
Figure 3. MALDI-ToF spectrum of PCL obtained from entry 4, Table 1 (1, 1000:1, melt, air). The main families are (i) chain polymer (terminated by 2 OH groups) as potassium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 39.1 (K+)], e.g., for n = 90, calc. 10,329.7 obsv. 10,327.3; (ii) cyclic polymers as the sodium adducts [M = n × 114.14(CL) + 22.99 (Na+)], e.g., calc. 10,295.6, n = 90, obsv. 10,296.5.
Figure 3. MALDI-ToF spectrum of PCL obtained from entry 4, Table 1 (1, 1000:1, melt, air). The main families are (i) chain polymer (terminated by 2 OH groups) as potassium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 39.1 (K+)], e.g., for n = 90, calc. 10,329.7 obsv. 10,327.3; (ii) cyclic polymers as the sodium adducts [M = n × 114.14(CL) + 22.99 (Na+)], e.g., calc. 10,295.6, n = 90, obsv. 10,296.5.
Catalysts 15 00261 g003
Catalysts 15 00261 g004
Figure 4. MALDI-ToF spectrum of PCL obtained from entry 7, Table 1 (1, 500:1 melt, N2). The main families are (i) chain polymer (terminated by 2 OH groups) as potassium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 39.1 (K+)], e.g., for n = 90, calc. 10,329.7 obsv. 10,328.0; (ii) cyclic polymers as the sodium adducts [M = n × 114.14(CL) + 22.99 (Na+)], e.g., calc. 10,295.6, n = 90, obsv. 10,298.5.
Figure 4. MALDI-ToF spectrum of PCL obtained from entry 7, Table 1 (1, 500:1 melt, N2). The main families are (i) chain polymer (terminated by 2 OH groups) as potassium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 39.1 (K+)], e.g., for n = 90, calc. 10,329.7 obsv. 10,328.0; (ii) cyclic polymers as the sodium adducts [M = n × 114.14(CL) + 22.99 (Na+)], e.g., calc. 10,295.6, n = 90, obsv. 10,298.5.
Catalysts 15 00261 g004
Catalysts 15 00261 g005
Figure 5. MALDI-ToF spectrum of PCL obtained from entry 16, Table 1 (2, 500:1 melt, air). The main families are (i) chain polymer (terminated by 2 OH groups, i.e., HO(C6H10O2)H) [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., for n = 70, calc. 8007.8 obsv. 8007.4; (ii) chain polymer (terminated by 2 OH groups) as sodium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., for n = 70, calc. 8030.8 obsv. 8032.0. (iii) A minor family can be assigned to chain polymers terminated by OMe/OH end groups as sodium adducts [M = 31 (OMe) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., calc. 8044.8, n = 70, obsv. 8048.3.
Figure 5. MALDI-ToF spectrum of PCL obtained from entry 16, Table 1 (2, 500:1 melt, air). The main families are (i) chain polymer (terminated by 2 OH groups, i.e., HO(C6H10O2)H) [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., for n = 70, calc. 8007.8 obsv. 8007.4; (ii) chain polymer (terminated by 2 OH groups) as sodium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., for n = 70, calc. 8030.8 obsv. 8032.0. (iii) A minor family can be assigned to chain polymers terminated by OMe/OH end groups as sodium adducts [M = 31 (OMe) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., calc. 8044.8, n = 70, obsv. 8048.3.
Catalysts 15 00261 g005
Catalysts 15 00261 g006
Figure 6. MALDI-ToF spectrum of PCL obtained from entry 22, Table 1 ([Sn(Oct)2], 500:1 melt, air). The main family is a chain polymer (terminated by 2 OH groups) as sodium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., for n = 35, calc. 4034.4 obsv. 4034.4; n = 70, calc. 8030.8 obsv. 8029.3.
Figure 6. MALDI-ToF spectrum of PCL obtained from entry 22, Table 1 ([Sn(Oct)2], 500:1 melt, air). The main family is a chain polymer (terminated by 2 OH groups) as sodium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., for n = 35, calc. 4034.4 obsv. 4034.4; n = 70, calc. 8030.8 obsv. 8029.3.
Catalysts 15 00261 g006
Catalysts 15 00261 g007
Figure 7. Kinetic runs using [ε-CL]:[cat] = 500:1 at 110 °C in toluene.
Figure 7. Kinetic runs using [ε-CL]:[cat] = 500:1 at 110 °C in toluene.
Catalysts 15 00261 g007
Catalysts 15 00261 g008
Figure 8. MALDI-ToF spectrum of PVL obtained from entry 3, Table 2 (1, 500:1, toluene, N2). The main family is composed of chain polymers (terminated by 2 OH groups) as sodium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., for n = 40, calc. 4046.6, obsv. 4044.5.
Figure 8. MALDI-ToF spectrum of PVL obtained from entry 3, Table 2 (1, 500:1, toluene, N2). The main family is composed of chain polymers (terminated by 2 OH groups) as sodium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., for n = 40, calc. 4046.6, obsv. 4044.5.
Catalysts 15 00261 g008
Catalysts 15 00261 g009
Figure 9. MALDI-ToF spectrum of PVL obtained from entry 10, Table 2 (2, 500:1 melt, N2). The main family is composed of chain polymers (terminated by 2 OH groups) as sodium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., for n = 40, calc. 4046.6 obsv. 4046.3.
Figure 9. MALDI-ToF spectrum of PVL obtained from entry 10, Table 2 (2, 500:1 melt, N2). The main family is composed of chain polymers (terminated by 2 OH groups) as sodium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., for n = 40, calc. 4046.6 obsv. 4046.3.
Catalysts 15 00261 g009
Catalysts 15 00261 g010
Figure 10. PVL obtained from entry 10, Table 2 (2, 500:1 melt, air). The main family is composed of chain polymers (terminated by OH/OMe groups) as sodium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., for n = 30, calc. 3059.2, obsv. 3061.2.
Figure 10. PVL obtained from entry 10, Table 2 (2, 500:1 melt, air). The main family is composed of chain polymers (terminated by OH/OMe groups) as sodium adducts [M = 17 (OH) + 1(H) + n × 114.14 (CL) + 22.99 (Na+)], e.g., for n = 30, calc. 3059.2, obsv. 3061.2.
Catalysts 15 00261 g010
Catalysts 15 00261 g011
Figure 11. Kinetic runs using [δ-VL]:[cat] = 500:1 at 110 °C in toluene.
Figure 11. Kinetic runs using [δ-VL]:[cat] = 500:1 at 110 °C in toluene.
Catalysts 15 00261 g011
Catalysts 15 00261 g012
Figure 12. TGAs of top 1∙2MeCN and bottom 2.
Figure 12. TGAs of top 1∙2MeCN and bottom 2.
Catalysts 15 00261 g012
Table 1. The ROP of ε-CL over 24 h catalysed by 1, 2 [Sn(Oct)2], and [Sn(OtBu)4)].
Table 1. The ROP of ε-CL over 24 h catalysed by 1, 2 [Sn(Oct)2], and [Sn(OtBu)4)].
EntryCat.[CL]:[Cat]T/°CConv a (%)Mn(obsv) bMn Corrected cMn,Cal dÐ b
11500:1130>9919,33010,84056,5204.95
2 e1500:1130>999150514056,2501.84
311000:11309187,06048,750103,8903.81
4 e11000:11308116,300913092,4701.64
51100:11309720,21011,32011,0902.28
6 e1100:1130997460418011,3201.87
7 f1500:1130>9918,30010,25056,5202.15
8 e,f1500:11309814,020785055,9501.80
91250:11309039,41022,07025,7002.01
10 e,f1250:1130>9913,840775028,2703.44
11 f1250:1130>9970,37039,41028,2702.01
121500:1150----
13 e1500:1150----
142500:1130>9947,70026,71056,5201.75
15 e2500:1130>9938,88021,77056,5201.48
16 f2500:11309127,58015,44051,9502.02
17 e,f2500:1130999570536056,5202.00
182500:11544----
19 e2500:11518----
20Sn(Oct)2500:11309955,53031,10056,5201.91
21 eSn(Oct)2500:11305610,730/34406010/193031,9801.21/1.11
22Sn(Oct)2500:11309221,12011,83052,5202.31
23 e,fSn(Oct)2500:1130>9910,920612056,5201.64
24Sn(Oct)2500:1150----
25 eSn(Oct)2500:1152----
26Sn(OtBu)4500:1150----
27 eSn(OtBu)4500:1150----
28Sn(OtBu)4500:1130>9957,94032,45056,5207.81
29 fSn(OtBu)4500:113099124,07069,48056,52023.9
a Determined by 1H NMR spectroscopy. b Measured by GPC in THF relative to polystyrene standards; c Mn calculated values after Mark–Houwink correction [53,54]; Mn corrected = 0.56 × Mn obsd. d Calculated from ([CL]0/[cat]0) × conv (%) × monomer molecular weight (MCL = 114.14) + end groups (H/OH used in this case). e Conducted in air. f Conducted as a melt.
Table 2. The ROP of δ-VL over 24 h catalysed by 1, 2 [Sn(Oct)2], and [Sn(OtBu)4)].
Table 2. The ROP of δ-VL over 24 h catalysed by 1, 2 [Sn(Oct)2], and [Sn(OtBu)4)].
EntryCat.[VL]:[Cat]T/°CConv a (%)MnbMn correctedMn,CalcÐ d
11500:115814400251040,5701.60
2 e1500:115803540202040,0702.57
31500:1130>997190410049,5803.24
4 e1500:1130>9913240754049,5801.07
5 f1500:11309317,390/32009910/182046,570 1.29/1.39
6 e,f1500:1130>995210297049,5801.61
72500:11308816,060/35609150/205044,0701.17/1.38
8 e2500:1130>9913,540772049,5801.60
9 f2500:1130946040338047,0702.20
10 e,f2500:1130999560545049,5802.14
112500:115783660209039,0602.39
12 e2500:115772860163038,5602.15
13Sn(Oct)2500:1130>998710496049,5801.99
14 eSn(Oct)2500:1130>998040458049,5801.65
15 fSn(Oct)2500:1130904130235045,0709.78
16 e,f Sn(Oct)2500:1130>996620377049,5802.15
17Sn(Oct)2500:115892740156044,5701.89
18 eSn(Oct)2500:115882450140044,0701.47
19Sn(OtBu)4500:115687540/42204300/2410 g34,0601.03/1.02
20 eSn(OtBu)4500:115512810/16401600/93025,5501.03/1.03
21Sn(OtBu)4500:1130>9977,97044,44049,5804.27
22fSn(OtBu)4500:1130>9938,89022,17049,5802.96
a Determined by 1H NMR spectroscopy. b Measured by GPC in THF relative to polystyrene standards; c Mn calculated values after Mark–Houwink correction [53,54]; Mn corrected = 0.57 × Mn obsd. d Calculated from ([VL]0/[cat]0) × conv (%) × monomer molecular weight (MVL = 100.12) + end groups (H/OH used in this case). e Conducted in air. f Conducted as a melt. g Lower Mnb peaks were also observed at 2480 (Ð 1.02) and 1380 (Ð 1.04).
Table 3. Crystallographic data for 1·2MeCN and 2.
Table 3. Crystallographic data for 1·2MeCN and 2.
Compound1∙2MeCN2
FormulaC64H54N6O8SnC32H28O10Sn
Formula weight1105.78691.23
Crystal systemTriclinicTetragonal
Space groupP1I-42d
Unit cell dimensions
a (Å)14.8890(3)21.0627(5)
b (Å)14.9289(3)21.0627(5)
c (Å)15.0152(3)14.9499(5)
α (°)114.697(2)90
β (°)104.025(2)90
γ (°)108.449(2)90
V (Å3)2590.53(10)6632.3(4)
Z28
Temperature (K)100(2)100(2)
Wavelength (Å)0.710751.54184
Calculated density
(gcm–3)		1.4181.385
Absorption coefficient
(mm–1)		0.5576.578
Crystal size (mm3)0.10 × 0.07 × 0.030.25 × 0.20 × 0.12
θ(max) (°)61.0140.0
Reflections measured66,61943,429
Unique reflections15,7483162
Rint0.0560.086
Number of parameters686195
R1 [F2 > 2σ(F2)]0.0490.074
wR2 (all data)0.1310.16
GOOF, S1.051.21
Largest difference
peak and hole (e Å−3)		2.61 and −0.610.65 and −1.10
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Prior, T.J.; Redshaw, C. Tin Complexes Derived from the Acids Ph2C(X)CO2H (X = OH, NH2): Structure and ROP Capability. Catalysts 2025, 15, 261. https://doi.org/10.3390/catal15030261

AMA Style

Prior TJ, Redshaw C. Tin Complexes Derived from the Acids Ph2C(X)CO2H (X = OH, NH2): Structure and ROP Capability. Catalysts. 2025; 15(3):261. https://doi.org/10.3390/catal15030261

Chicago/Turabian Style

Prior, Timothy J., and Carl Redshaw. 2025. "Tin Complexes Derived from the Acids Ph2C(X)CO2H (X = OH, NH2): Structure and ROP Capability" Catalysts 15, no. 3: 261. https://doi.org/10.3390/catal15030261

APA Style

Prior, T. J., & Redshaw, C. (2025). Tin Complexes Derived from the Acids Ph2C(X)CO2H (X = OH, NH2): Structure and ROP Capability. Catalysts, 15(3), 261. https://doi.org/10.3390/catal15030261

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