New pre-catalysts for ring opening of lactides/lactones based on earth abundant metals

In this study, a number of Nb, Ta, Mo, V, Al, Li and Zn complexes have been synthesised and fully characterised. The catalytic behavior of these pre-catalysts towards the ring opening polymerization (ROP) of the cyclic esters is discussed.Chapter 1 Presents an introduction to the history of polymers (from polyethylene to biodegradable polymers from cyclic esters), early discovery, mechanism of ring opening polymerisation and the use of vanadium, niobium, tantalum and molybdenum, aluiminium, lithium and zinc complexes as polymerization catalysts.Chpter 2 This chapter discussed results when the pre-ligands α,α,α’,α’-tetra(3,5-di-tert-butyl-2-hydroxyphenyl-p-)xylene-para-tetraphenol(p-L¹H₄) and α,α,α’,α’tetra (3,5-di-tert-butyl-2-hydroxyphenyl-m-)xylene-meta-tetraphenol (m-L²H₄) are reacted with a number of niobium and tantalum precursors such as [NbCl₅], [TaCl₅] or [Nb(O)Cl₃(NCMe)₂]. The resulting products {[NbCl₃(NCMe)]₂(μ-p-L¹)}·6MeCN (1·6MeCN), {[NbCl₂(OEt)(NCMe)]₂(μ-p-L¹)}·3½MeCN·0.614 toluene (2·3½MeCN·0.614 toluene), {[TaCl₂(OEt)(NCMe)]₂(μ-p-L¹)}.5MeCN (3·5MeCN), {[Nb(NCMe)Cl(m-L²H₂)₂]}·3½MeCN(4·3½MeCN) and {[Nb(NCMe)Cl(m-L²H₂)₂]}·5MeCN (4·5MeCN) were structurally characterized. Complexes 1–4 were screened as pre-catalysts for the ROP of ε-caprolactone, both with and without benzyl alcohol or solvent present, and at various temperatures.Chapter 3 In this chapter, the reaction of the bulky bi-phenols 2,2′-RCH[4,6-(t-Bu)₂C₆H₂OH]₂ (R = Me L³MeH₂, Ph L⁴PhH₂) with the bis(imido) molybdenum(VI) tert-butoxides [Mo(NR¹)(NR²)(Ot-Bu)₂] (R¹ = R² = 2,6-C₆H₃-i-Pr2; R¹ = t-Bu, R² = C₆F₅) has been studied. The complexes [Mo(NC₆H₃i-Pr₂-2,6)2L3Me] (5), [Mo(NC₆H₃i-Pr₂-2,6)2L⁴Ph] (6) and [Mo(Nt-Bu)(μ-NC₆F₅)(L³Me)]₂ (7) were isolated. Similar use of the tri-phenol 2,6-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-4-methylphenol (L⁵H₃) with [Mo(NC₆H₃i-Pr₂-2,6)₂(Ot-Bu)₂] afforded the oxo-bridged product [Mo(NC6H₃i-Pr₂-2,6)(NCMe)(μ-O)L5H]₂ (8), whilst use of the tetra-phenols L¹pH₄/L²mH₄ led to {[Mo(NC₆H₃i-Pr₂-2,6)₂]₂(μ-L¹p)} (9) or {[Mo(NC₆H₃i-Pr₂-2,6)₂]₂(μ-L²m)}(10), respectively. Similar use of [Mo(NC₆F5)2(Ot-Bu)₂] with L¹pH₄ afforded {[Mo(NC₆F₅)(Ot-Bu)₂]₂(μ-L¹p)}·6MeCN (11·6MeCN). The molecular structures of 5, 6·CH₂Cl₂, 7, 8·6MeCN, 10·2C₆H14, and 11·6MeCN are reported. These complexes have been screened for their ability to act as catalysts for the ROP of ε-caprolactone; for comparative studies the complex [Mo(NC₆H₃i-Pr₂ 2,6)₂Cl₂(DME) (12) has also been screened.Chpter 4 This chapter focuses on the use of the vanadyl complexes. The new complexes [VO(Ot-Bu)L³] (13), {[VO(Oi-Pr)]₂(µ-p-L¹p)} (14) {[VO(OR)]₂(µ-p-L²m)} (R = i-Pr 15, t-Bu 16 have been prepared from [VO(OR)₃] (R = n-Pr, i-Pr or t-Bu) and the respective phenol, namely 2,2/-ethylidenebis(4,6-di-tert-butylphenol) (L³H₂) or Lp/mH4. For comparative studies, the known complexes [VO(µ-On-Pr)L³]₂ (18), [VOL⁶]₂ (19) (L6H₃ 2,6-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-4-tert-butylphenol) were prepared. An imido complex {[VCl(Np-tolyl)(NCMe)]₂(μ-p-L¹p)} (17) has also been prepared. The molecular structures of complexes 13 – 19 are reported, and these complexes 13 – 19 have been screened for their ability to ring open polymerise ε-caprolactone, L-lactide or rac-lactide with and without solvent present. The co-polymerization of ε-caprolactone with L-lactide or rac-lactide was also studied.Chapter 5 describes the reaction of R¹R²CHN=CH(3,5-t-Bu₂C₆H₂-OH-2) (R¹ = R² = Me L⁷H; R¹ = Me, R² = Ph L⁸H; R¹ = R² = Ph L⁹H) with slightly greater than one equivalent of R³₃Al (R³ = Me, Et), which afforded the complexes [(L⁷⁻⁹)AlR³₂] (L⁷, R³ = Me 20, R³ = Et 21; L⁸, R³ = Me 22, R³ = Et 23; L³, R³ = Me 24, R³ = Et 25); complex 20 has been previously reported. Use of the N,O-ligand derived from 2,2/-diphenylglycine afforded either 24 or an amine by-product [Ph₂NCH₂(3,5-t-Bu₂C₆H₂-O-2)AlMe₂] (26). The known Schiff base complex [2-Ph₂PC₆H4CH₂(3,5-t-Bu₂C₆H₂-O-2)AlMe₂] (27) and the product of the reaction of 2-diphenylphosphinoaniline 1-NH₂,2-PPh₂C₆H₄ with Me₃Al, namely {Ph₂PC₆H₄N[(Me₂Al)₂µ-Me](µ-Me₂Al)} (28) were also isolated. For structural and catalytic comparisons, complexes resulting from interaction of Me₃Al with diphenylamine or benzhydrylamine, namely {Ph₂N[(Me₂Al)₂-Me]} (29) and [Ph₂CHNH(µ-Me₂Al)]₂·MeCN (30), were prepared. The molecular structures of the Schiff pro-ligands derived from Ph₂CHNH₂ and 2,2/-Ph₂C(CO₂H)(NH₂), together with complexes 24, 26 and 28 - 30·MeCN were determined. All complexes were screened for their ability to ROP ε-caprolactone, δ-valerolactone or rac-lactide, in the presence of benzyl alcohol, with or without solvent present.Chapter 6 describes the reaction of lithium alkoxides LiOR (R = t-Bu, Ph) with the acids 2,2/-Ph₂C(X)(CO₂H), where X = OH, NH₂, i.e. benzilic acid (2,2/-diphenylglycolic acid, benzH) or 2,2/-diphenylglycine (dpgH). In the case of benzH, reaction with one equivalent of LiOt-Bu in THF afforded the complex [Li(benz)(THF)]₂·2THF (31·2THF), which adopts a 1D chain structure. If acetonitrile is employed in the work-up under mild conditions, another solvate of 31 is isolated; use of LiOPh also lead to 31. Use of more robust work-up conditions afforded the complex [Li7(benz)7(MeCN)] (32·2MeCN·THF). Increasing the amount of LiOt-Bu (2 equivalents) led to the isolation of the complex {Li8(Ot-Bu)₂[(benz)](OCPh₂CO₂-CPh₂CO₂t-Bu)₂(THF)₄} (33). In the case of dpgH, use of two equivalents of LiOt-Bu in THF afforded [Li₆(Ot-Bu)₂(dpg)₂(THF)₂] (34), which contains an Li₂O₂ 6-step ladder. Similar reaction of lithium phenoxide with dpg afforded the complex [Li8(PhO)₄(dpg)₄(MeCN)₄] (35). The molecular structures of complexes 31 - 35 are reported; all were screened for their potential to act as pre-catalysts for ROP of ε-caprolactone (ε-CL), rac-lactide (r-LA) and δ-valerolactone (δ-VL).Chapter 7 describes the reaction of the dialkylzinc reagents R2Zn with the acids 2,2-Ph₂C(X)(CO₂H), where X = NH₂, OH, ie 2,2/-diphenylglycine (dpgH) or benzilic acid (benzH₂). With dpgH, the tetra-nuclear ring complexes [RZn(dpg)]₄, where R = Me (36), Et (37), 2-CF₃C₆H₄ (38), 2,4,6-F₃C₆H₂ (39) were isolated; complex 37 has been previously reported. The crystal structures of 36·2MeCN, 37 and 38·4(C7H8) ·1.59(H₂O) are reported, along with that of the intermediate compound (2-CF₃C₆H₄)₃B·MeCN and the known compound [ZnCl₂(NCMe)₂]. Complexes 36– 39, together with the known [(ZnEt)₃(ZnL)₃(benz)₃] (40; L = MeCN), have been screened, in the presence and absence of benzyl alcohol, for their potential to act as catalysts for the ROP of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL) and rac-lactide (rac-LA); the co-polymerization of ε-CL with rac-LA was also studied.Chapter 8 This chapter presents the experimental section.Chapter 9 Appendix

Molybdenum (VI) imido complexes derived from chelating phenols : Synthesis, characterization and ɛ-Caprolactone ROP capability

Reaction of the bulky bi-phenols 2,2′-RCH[4,6-(t-Bu)₂C₆H₂OH]₂ (R = Me L¹ᵐᵉH₂, Ph L¹ᵖʰH₂) with the bis(imido) molybdenum(VI) tert-butoxides [Mo(NR¹)(NR²)(Ot-Bu)₂] (R¹ = R² = 2,6-C₆H₃-i-Pr₂; R¹ = t-Bu, R² = C₆F₅) afforded, following the successive removal of tert-butanol, the complexes [Mo(NC₆H₃ᵢ-Pr₂-2,6)₂L¹ᵐᵉ] (1), [Mo(NC₆H₃i-Pr₂-2,6)₂L¹ᵖʰ] (2) and [Mo(Nt-Bu)(μ-NC₆F₅)(L¹ᵐᵉ)]₂ (3). Similar use of the tri-phenol 2,6-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-4-methylphenol (L²H₃) with [Mo(NC₆H₃ᵢ-Pr₂-2,6)₂(Ot-Bu)₂] afforded the oxo-bridged product [Mo(NC₆H₃i-Pr₂-2,6)(NCMe)(μ-O)L2H]₂ (4), whilst use of the tetra-phenols α,α,α′,α′-tetrakis(3,5-di-tert-butyl-2-hydroxyphenyl)-p- or -m-xylene L³ᵖH₄/L³ᵐH₄ led to {[Mo(NC₆H₃ᵢ-Pr₂-2,6)₂]₂(μ-L³ᵖ)} (5) or {[Mo(NC₆H₃ᵢ-Pr₂-2,6)₂]₂(μ-L³ᵐ)} (6), respectively. Similar use of [Mo(NC₆F₅)₂(Ot-Bu)₂] with L³ᵖH₄ afforded, after work-up, the complex {[Mo(NC₆F₅)(Ot-Bu)₂]₂(μ-L³ᵖ)}·6MeCN (7·6MeCN). Molecular structures of 1, 2·CH₂Cl₂, 3, 4·6MeCN, 6·2C₆H₁₄, and 7·6MeCN are reported and these complexes have been screened for their ability to ring open polymerize (ROP) ε-caprolactone; for comparative studies the precursor complex [Mo(NC₆H₃ᵢ-Pr₂-2,6)₂Cl₂(DME)] (DME = 1,2-dimethoxyethane) has also been screened. Results revealed that good activity is only achievable at temperatures of ≥100 °C over periods of 1 h or more. Polymer polydispersities were narrow, but observed molecular weights (Mn) were much lower than calculated values

Tetraphenolate niobium and tantalum complexes for the ring opening polymerization of ε-caprolactone

Reaction of the pro-ligand α,α,α′,α′-tetra(3,5-di-tert-butyl-2-hydroxyphenyl-p-)xylene-para-tetraphenol (p-L¹H₄) with two equivalents of [NbCl₅] in refluxing toluene afforded, after work-up, the complex {[NbCl₃(NCMe)]₂(μ-p-L¹)}·6MeCN (1·6MeCN). When the reaction was conducted in the presence of excess ethanol, the orange complex {[NbCl₂(OEt)(NCMe)]₂(μ-p-L¹)}·3½MeCN·0.614toluene (2·3½MeCN·0.614toluene) was formed. A similar reaction using [TaCl₅] afforded the yellow complex {[TaCl₂(OEt)(NCMe)]₂(μ-p-L¹)}·5MeCN (3·5MeCN). In the case of the meta pro-ligand, namely α,α,α′,α′tetra(3,5-di-tert-butyl-2-hydroxyphenyl-m-)xylene-meta-tetraphenol (m-L²H₄) only the use of [Nb(O)Cl₃(NCMe)₂] led to the isolation of crystalline material, namely the orange bis-chelate complex {[Nb(NCMe)Cl(m-L²H₂)₂]}·3½MeCN (4·3½MeCN) or {[Nb(NCMe)Cl(m-L²H₂)₂]}·5MeCN (4·5MeCN). The molecular structures of 1–4 and the tetraphenols L¹H₄ and m-L²H₄·2MeCN have been determined. Complexes 1–4 have been screened as pre-catalysts for the ring opening polymerization of ε-caprolactone, both with and without benzyl alcohol or solvent present, and at various temperatures; conversion rates were mostly excellent (>96%) with good control either at >100 °C over 20 h (in toluene) or 1 h (neat)

Ring opening polymerization of lactides and lactones by multimetallic alkyl zinc complexes derived from the acids Ph₂C(X)CO₂2H (X = OH, NH₂ )

The reaction of the dialkylzinc reagents R₂Zn with the acids 2,2-Ph₂C(X)(CO₂H), where X = NH₂, OH, i.e. 2,2′-diphenylglycine (dpgH) or benzilic acid (benzH2), in toluene at reflux temperature afforded the tetra-nuclear ring complexes [RZn(dpg)]₄, where R = Me (1), Et (2), 2-CF₃C₆H₄ (3), and 2,4,6-F₃C₆H₂ (4); complex 2 has been previously reported. The crystal structures of 1·(2MeCN), 3 and 4·(4(C₇H₈)·1.59(H₂O)) are reported, along with that of the intermediate compound (2-CF₃C₆H₄)3B·MeCN and the known compound [ZnCl₂(NCMe)₂]. Complexes 1–4, together with the known complex [(ZnEt)₃(ZnL)₃(benz)₃] (5; L = MeCN), have been screened, in the absence of benzyl alcohol, for their potential to act as catalysts for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL) and rac-lactide (rac-LA); the co-polymerization of ε-CL with rac-LA was also studied. Complexes 3 and 4 bearing fluorinated aryls at zinc were found to afford the highest activities

Multimetallic lithium complexes derived from the acids Ph₂C(X)CO₂H (X = OH, NH₂) : synthesis, structure and ring opening polymerization of lactides and lactones

Reaction of LiOR (R=t-Bu, Ph) with the acids 2,2/-Ph₂C(X)(CO₂H), X=OH (benzH), NH₂ (dpgH) was investigated. For benzH, one equivalent LiOt-Bu in THF afforded [Li(benz)]2⋅2THF (1⋅2THF), which adopts a 1D chain structure. If acetonitrile is used (mild conditions), another polymorph of 1 is isolated; LiOPh also led to 1. Robust work-up afforded [Li₇(benz)₇(MeCN)] 2MeCN THF (2⋅2MeCN⋅THF). Use of LiOt-Bu (2 equivalents) led to {Li₈(Ot-Bu)₂[(benz)](OCPh₂CO₂CPh₂CO2t-Bu)₂(THF)₄} (3), the core of which comprises two open cubes linked by benz ligands. For dpgH, two equivalents of LiOt-Bu in THF afforded [Li6(Ot-Bu)₂(dpg)₂(THF)₂] (4), which contains an Li₂Ov 6-step ladder. Similar reaction of LiOPh afforded [Li₈(PhO)₄(dpg)₄(MeCN)₄] (5). Complexes 1–5 were screened for their potential as catalysts for ring opening polymerization (ROP) of ϵ-caprolactone (ϵ-CL), rac-lactide (rac-LA) and δ-valerolactone (δ-VL). For ROP of ϵ-CL, conversions > 70 % were achievable at 110 °C with good control. For rac-LA and δ-VL, temperatures of at least 110 °C over 12 h were necessary for activity (conversions > 60 %). Systems employing 2 were inactiv

Membrane Computing for Real Medical Image Segmentation

In this paper, membrane-based computing image segmentation, both region-based and edge-based, is proposed for medical images that involve two types of neighborhood relations between pixels. These neighborhood relations—namely, 4-adjacency and 8-adjacency of a membrane computing approach—construct a family of tissue-like P systems for segmenting actual 2D medical images in a constant number of steps; the two types of adjacency were compared using different hardware platforms. The process involves the generation of membrane-based segmentation rules for 2D medical images. The rules are written in the P-Lingua format and appended to the input image for visualization. The findings show that the neighborhood relations between pixels of 8-adjacency give better results compared with the 4-adjacency neighborhood relations, because the 8-adjacency considers the eight pixels around the center pixel, which reduces the required communication rules to obtain the final segmentation results. The experimental results proved that the proposed approach has superior results in terms of the number of computational steps and processing time. To the best of our knowledge, this is the first time an evaluation procedure is conducted to evaluate the efficiency of real image segmentations using membrane computing

Vanadium(v) phenolate complexes for ring opening homo- and co-polymerisation of ε-caprolactone, L-lactide and rac-lactide

The vanadyl complexes [VO(OtBu)L¹ ] (1) and {[VO(OiPr)]₂ (μ-p-L²ᵖ)} (2) {[VO(OR)]₂ (μ-p-L²ᵐ )} (R = iPr 3, tBu 4) have been prepared from [VO(OR)₃ ] (R = nPr, iPr or tBu) and the respective phenol, namely 2,2′-ethylidenebis(4,6-di-tert-butylphenol) (L¹ H₂ ) or α,α,α′,α′-tetra(3,5-di-tert-butyl-2-hydroxyphenyl–p/m-)xylene-para-tetraphenol (L2p/mH₄). For comparative studies, the known complexes [VO(μ-OnPr)L¹]₂ (I), [VOL³ ]₂ (II) (L³H₃ = 2,6-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-4-tert-butylphenol) were prepared. An imido complex {[VCl(Np-tolyl)(NCMe)]₂(μ-p-L²ᵖ)} (5) has been prepared following work-up from [V(Np-tolyl)Cl₃ ], L²ᵖH₄ and Et₃ N. The molecular structures of complexes 1–5 are reported. Complexes 1–5 and I and II have been screened for their ability to ring open polymerise ε-caprolactone, L-lactide or rac-lactide with and without solvent present. The co-polymerization of ε-caprolactone with L-lactide or rac-lactide afforded co-polymers with low lactide content; the reverse addition was ineffective

Organoaluminium complexes derived from Anilines or Schiff bases for ring opening polymerization of epsilon-caprolactone, delta-valerolactone and rac-lactide

Reaction of R¹R²CHN=CH(3,5-tBu₂C₆H₂-OH-2) (R¹ = R² = Me L¹H; R¹ = Me, R² = Ph L²H; R¹ = R2 = Ph L³H) with one equivalent of R³3Al (R³ = Me, Et) afforded [(L¹-³)AlR³₂] (L¹, R³ = Me 1, R³ = Et 2; L², R³ = Me 3, R³ = Et 4; L³ R³ = Me 5, R³ = Et 6); complex 1 has been previously reported. Use of the N,O-ligand derived from 2,2/-diphenylglycine afforded either 5 or a by-product [Ph₂NCH₂(3,5-tBu₂C₆H₂-O-2)AlMe₂] (7). The known Schiff base complex [2-Ph₂PC₆H4CH₂(3,5-tBu₂C₃H₂-O-2)AlMe₂] (8) and the product of the reaction of 2-diphenylphosphinoaniline 1-NH₂,2-PPh₂C₆H4 with Me3Al, namely {Ph₂PC₆H4N[(Me₂Al)₂mu-Me](mu-Me₂Al)} (9) were also isolated. For structural and catalytic comparisons, complexes resulting from interaction of Me₃Al with diphenylamine or benzhydrylamine, namely {Ph₂N[(Me₂Al)2mu-Me]} (10) and [Ph₂CHNH(mu-Me₂Al)]₂·MeCN (11), were prepared. The molecular structures of the Schiff pro-ligands derived from Ph₂CHNH₂ and 2,2/-Ph2C(CO₂H)(NH₂), together with complexes 5, 7 and 9 - 11·MeCN were determined. All complexes have been screened for their ability to ring opening polymerization (ROP) epsilon-caprolactone, delta-valerolactone or rac-lactide, in the presence of benzyl alcohol, with or without solvent present. The co-polymerization of epsilon-caprolactone with rac-lactide has also been studied

Multimetallic lithium complexes derived from the acids Ph 2 C(X)CO 2 H (X=OH, NH 2 ): Synthesis, structure and ring opening polymerization of lactides and lactones

Reaction of LiOR (R = t-Bu, Ph) with the acids 2,2/-Ph2C(X)(CO2H), X = OH (benzH), NH2 (pdgH) was investigated. For benzH, one equivalent LiOt-Bu in THF afforded [Li(benz)(THF)]2·2THF (1·2THF), which adopts a 1D chain structure. If acetonitrile is used (mild conditions), another solvate of 1 is isolated; LiOPh also led to 1. Robust work-up afforded [Li7(benz)7(MeCN)] (2·2MeCN·THF). Use of LiOt-Bu (2 equivalents) led to {Li8(Ot-Bu)2[(benz)](OCPh2CO2CPh2CO2t-Bu)2(THF)4} (3), the core of which comprises two open cubes linked by benz ligands. For dpgH, two equivalents of LiOt-Bu in THF afforded [Li6(Ot-Bu)2(dpg)2(THF)2] (4), which contains an Li2O2 6-step ladder. Similar reaction of LiOPh afforded [Li8(PhO)4(dpg)4(MeCN)4] (5). Complexes 1 - 5 were screened for their potential as catalysts for ring opening polymerization (ROP) of ε-caprolactone (ε-CL), rac-lactide (rac-LA) and δ-valerolactone (δ-VL). For ROP of ε-CL, conversions > 70% were achievable at 110 oC with good control. For rac-LA and δ-VL, temperatures of at least 110 oC over 12h were necessary for activity (conversions > 60%). Systems employing 2 were inactive

Organoaluminium complexes derived from anilines or Schiff bases for the ring-opening polymerization of ε-Caprolactone, δ-Valerolactone and rac-Lactide

Reaction of R1R2CHN=CH(3,5-tBu2C6H2-OH-2) (R1 = R2 = Me L1H; R1 = Me, R2 = Ph L2H; R1 = R2 = Ph L3H) with slightly greater than one equivalent of R33Al (R3 = Me, Et) afforded the complexes [(L1–3)AlR32] (L1, R3 = Me 1, R3 = Et 2; L2, R3 = Me 3, R3 = Et 4; L3 R3 = Me 5, R3 = Et 6); complex 1 has been previously reported. Use of the N,O-ligand derived from 2,2′-diphenylglycine afforded either 5 or the byproduct [Ph2NCH2(3,5-tBu2C6H2-O-2)AlMe2] (7). The known Schiff base complex [2-Ph2PC6H4CH2(3,5-tBu2C6H2-O-2)AlMe2] (8) and the product of the reaction of 2-diphenylphosphinoaniline 1-NH2,2-PPh2C6H4 with Me3Al, namely {Ph2PC6H4N[(Me2Al)2µ-Me](µ-Me2Al)} (9), were also isolated. For structural and catalytic comparisons, complexes resulting from the interaction of Me3Al with diphenylamine (or benzhydrylamine), namely {Ph2N[(Me2Al)2µ-Me]} (10) and [Ph2CHNH(µ-Me2Al)]2·MeCN (11), were prepared. The molecular structures of the Schiff proligands derived from Ph2CHNH2 and 2,2′-Ph2C(CO2H)(NH2), together with those of complexes 5, 7 and 9–11·MeCN were determined; 5 contains a chelating imino/phenoxide ligand, whereas 7 contains the imino function outside of the metallocyclic ring. Complex 9 contains three nitrogen-bound Al centres, two of which are linked by a methyl bridge, whilst the third bridges the N and P centres. In 10, the structure resembles 9 with a bridging methyl group, whereas the introduction of the extra carbon in 11 results in the formation of a dimer. All complexes have been screened for their ability to promote the ring-opening polymerization (ROP) ε-caprolactone, δ-valerolactone or rac-lactide, in the presence of benzyl alcohol, with or without solvent present. Reasonable conversions were achievable at room temperature for ε-caprolactone when using complexes 7, 9 and 12, whilst at higher temperatures (80–110 °C), all complexes produced good (> 65 %) to quantitative conversions over periods as short as 3 min, albeit with poor control. In the absence of solvent, conversions were nearly quantitative at 80 °C in 5 min with better agreement between observed and calculated molecular weight (Mn). For rac-lactide, conversions were typically in the range 71–86 % at 110 °C in 12 h, with poor control affording atactic polylactide (PLA), whilst for δ-valerolactone more forcing conditions (12–24 h at 110 °C) were required for high conversion. Co-polymerization of ε-caprolactone with rac-lactide afforded co-polymers with appreciable lactide content (35–62.5 %); the reverse addition was ineffective, affording only (polycaprolactone) PCL