Synthesis of Nonisocyanate Poly(hydroxy)urethanes from Bis(cyclic carbonates) and Polyamines.

Nonisocyanate polyurethane materials with pending alcohol groups in the polymeric chain were synthesized by polyaddition reaction of bis(cyclic carbonates) onto diamines. For the platform molecule, 1,4-butanediol bis(glycidyl ether carbonate) (BGBC, 1) was used. The polyaddition reaction of 1 onto a wide range of diamines with different electronic and physical properties was explored. All PHUs were obtained quantitatively after 16 h at 80 °C temperature in MeCN as solvent. The low nucleophilicity of L-lysine has proven unable to ring-open the cyclic carbonate and, thus, no reaction occurred. The addition of DBU or TBD as the catalyst was tested and allows the obtention of the desired PHU. However, the presence of strong bases also led to the formation of polyurea fragments in the new PHU. The different poly(hydroxyurethane) materials were characterized using a wide range of spectroscopic techniques such as NMR, IR, MALDI-ToF, and using GPC studies. The thermal properties of the NIPUs were investigated by DSC and TGA analyses. Moreover, reactions employing different monomer ratios were performed, obtaining novel hydroxycarbamate compounds. Finally, sequential and one-pot experiments were also carried out to synthesize the PHUs polymers in one-step reaction.

Efficient Bulky Organo-Zinc Scorpionates for the Stereoselective Production of Poly(rac-lactide)s.

The direct reaction of the highly sterically demanding acetamidinate-based NNN'-scorpionate protioligand Hphbptamd [Hphbptamd = N,N'-di-p-tolylbis(3,5-di-tertbutylpyrazole-1-yl)acetamidine] with one equiv. of ZnMe2 proceeds in high yield to the mononuclear alkyl zinc complex [ZnMe(κ3-phbptamd)] (1). Alternatively, the treatment of the corresponding lithium precursor [Li(phbptamd)(THF)] with ZnCl2 yielded the halide complex [ZnCl(κ3-phbptamd)] (2). The X-ray crystal structure of 1 confirmed unambiguously a mononuclear entity in these complexes, with the zinc centre arranged with a pseudotetrahedral environment and the scorpionate ligand in a κ3-coordination mode. Interestingly, the inexpensive, low-toxic and easily prepared complexes 1 and 2 resulted in highly efficient catalysts for the ring-opening polymerisation of lactides, a sustainable bio-resourced process industrially demanded. Thus, complex 1 behaved as a single-component robust initiator for the living and immortal ROP of rac-lactide under very mild conditions after a few hours, reaching a TOF value up to 5520 h-1 under bulk conditions. Preliminary kinetic studies revealed apparent zero-order dependence on monomer concentration in the absence of a cocatalyst. The PLA materials produced exhibited narrow dispersity values, good agreement between the experimental Mn values and monomer/benzyl alcohol ratios, as well as enhanced levels of heteroselectivity, reaching Ps values up to 0.74.

Ring-Opening Copolymerization of Cyclohexene Oxide and Cyclic Anhydrides Catalyzed by Bimetallic Scorpionate Zinc Catalysts.

The catalytic activity and high selectivity reported by bimetallic heteroscorpionate acetate zinc complexes in ring-opening copolymerization (ROCOP) reactions involving CO2 as substrate encouraged us to expand their use as catalysts for ROCOP of cyclohexene oxide (CHO) and cyclic anhydrides. Among the catalysts tested for the ROCOP of CHO and phthalic anhydride at different reaction conditions, the most active catalytic system was the combination of complex 3 with bis(triphenylphosphine)iminium as cocatalyst in toluene at 80 °C. Once the optimal catalytic system was determined, the scope in terms of other cyclic anhydrides was broadened. The catalytic system was capable of copolymerizing selectively and efficiently CHO with phthalic, maleic, succinic and naphthalic anhydrides to afford the corresponding polyester materials. The polyesters obtained were characterized by spectroscopic, spectrometric, and calorimetric techniques. Finally, the reaction mechanism of the catalytic system was proposed based on stoichiometric reactions.

Efficient Synthesis of Cyclic Carbonates from Unsaturated Acids and Carbon Dioxide and their Application in the Synthesis of Biobased Polyurethanes.

Bio-derived furan- and diacid-derived cyclic carbonates have been synthesized in high yields from terminal epoxides and CO2 . Furthermore, four highly substituted terpene-derived cyclic carbonates were isolated in good yields with excellent diastereoselectivity in some cases. Eleven new cyclic carbonates derived from 10-undecenoic acid under mild reaction conditions were prepared, providing the corresponding carbonate products in excellent yields. The catalyst system also performed the conversion of an epoxidized fatty acid n-pentyl ester into a cyclic carbonate under relatively mild reaction conditions (80 °C, 20 bar, 24 h). This bis(cyclic carbonate) was obtained in high yields and with different cis/trans ratios depending on the co-catalyst used. An allyl alcohol by-product was only observed as a minor product when bis(triphenylphosphine)iminium chloride was used as co-catalyst. Finally, two cyclic carbonates were used as building blocks for the preparation of non-isocyanate poly(hydroxy)urethanes by reaction with 1,4-diaminobutane.

Zinc-Catalyzed Hydroalkoxylation/Cyclization of Alkynyl Alcohols.

Despite the great interest in zinc catalysis for hydroelementation reactions, the use of zinc complexes as catalysts for the hydroalkoxylation of alkynyl alcohols has not been reported to date. Scorpionate zinc complexes have been successfully designed as precatalysts for the hydroalkoxylation reaction of alkynyl alcohols under mild reaction conditions. Zinc amide complex 8 has been shown to be an excellent precatalyst for the highly selective intramolecular hydroalkoxylation process to yield the corresponding exocyclic enol ethers. Kinetic studies have been performed and confirmed that reactions are first-order in [catalyst] and zero-order in [alkynyl alcohol]. NMR spectroscopy and X-ray diffraction analysis provided evidence for the formation of an alkynyl zinc compound which has been shown to be a key intermediate in the hydroalkoxylation process. On the basis of the experimental results, a catalytic cycle is proposed.

Efficient Production of Poly(Cyclohexene Carbonate) via ROCOP of Cyclohexene Oxide and CO2 Mediated by NNO-Scorpionate Zinc Complexes.

New mono- and dinuclear chiral alkoxide/thioalkoxide NNO-scorpinate zinc complexes were easily synthesized in very high yields, and characterized by spectroscopic methods. X-ray diffraction analysis unambiguously confirmed the different nuclearity of the new complexes as well as the variety of coordination modes of the scorpionate ligands. Scorpionate zinc complexes 2, 4 and 6 were assessed as catalysts for polycarbonate production from epoxide and carbon dioxide with no need for a co-catalyst or activator under mild conditions. Interestingly, at 70 °C, 10 bar of CO2 pressure and 1 mol % of loading, the dinuclear thioaryloxide [Zn(bpzaepe)2{Zn(SAr)2}] (4) behaves as an efficient and selective one-component initiator for the synthesis of poly(cyclohexene carbonate) via ring-opening copolymerization of cyclohexene oxide (CHO) and CO2, affording polycarbonate materials with narrow dispersity values.

NNC-Scorpionate Zirconium-Based Bicomponent Systems for the Efficient CO2 Fixation into a Variety of Cyclic Carbonates.

Two new derivatives of the bis(3,5-dimethylpyrazol-1-yl)methane modified by introduction of organosilyl groups on the central carbon atom, one of which bearing a chiral fragment, have been easily prepared. We verified the potential utility of these compounds through the reaction with [Zr(NMe2)4] for the preparation of novel zirconium complexes in which an ancillary bis(pyrazol-1-yl)methanide acts as a robust monoanionic tridentate scorpionate in a κ3-NNC chelating mode, forming strained four-membered heterometallacycles. These κ3-NNC-scorpionate zirconium amides were investigated as catalysts in combination with tetra-n-butylammonium bromide as cocatalyst for CO2 fixation into five-membered cyclic carbonate products. The study has led to the development of an efficient zirconium-based bicomponent system for the selective cycloaddition reaction of CO2 with epoxides. Kinetics investigations confirmed apparent first-order dependence on the catalyst and cocatalyst concentrations. In addition, this system displays very broad substrate scope, including mono- and disubstituted substrates, as well as the challenging biorenewable terpene derived limonene oxide, under mild and solvent-free conditions.

Bimetallic Zinc Catalysts for Ring-Opening Copolymerization Processes.

Novel bimetallic zinc acetate complexes supported by heteroscorpionate ligands have been developed for the ring-opening copolymerization of cyclohexene oxide and CO2 and the terpolymerization of cyclohexene oxide, phthalic anhydride, and CO2. Heteroscorpionate ligands precursors L1-L3 were reacted with two equivalents of zinc acetate to afford the dinuclear zinc complexes [{Zn(κ3-bpzappe)}(µ-O2CCH3)3-{Zn(HO2CCH3)}] (1), [{Zn(κ3-bpzbdmape)}(µ-O2CCH3)3-{Zn(HO2CCH3)}] (2), and [{Zn(κ3-bpzbdeape)}(µ-O2CCH3)3{Zn(HO2CCH3)}] (3) in excellent yields. The molecular structure of these compounds was determined spectroscopically and confirmed by X-ray diffraction analysis. Zinc acetate complexes 1-3 were screened as catalysts for the copolymerization of cyclohexene oxide and CO2 to produce poly(cyclohexene)carbonate, and complex 3 was found to be the most active catalyst for this process in the absence of a cocatalyst. Furthermore, the terpolymerization of cyclohexene oxide, phthalic anhydride, and CO2 was studied using the combination of complex 3 and 4-dimethylaminopyridine as catalyst system yielding the corresponding polyester-polycarbonate materials.

Synthesis of an enantiopure scorpionate ligand by a nucleophilic addition to a ketenimine and a zinc initiator for the isoselective ROP of rac-lactide.

A novel nucleophilic addition of an organolithium to a ketenimine to prepare an enantiopure NNN-heteroscorpionate ligand is described. We verified its potential utility as a valuable scaffold for chirality induction through the preparation of enantiopure zinc complexes, which behave as highly efficient initiators to produce highly-enriched isotactic poly(lactide)s (Pi up to 0.88).

Efficient CO2 fixation into cyclic carbonates catalyzed by NNO-scorpionate zinc complexes.

A series of new chiral zwitterionic NNO-scorpionate mononuclear zinc alkyls [Zn(R)(κ3-NNO)]Br was developed in very high yields via suitable quaternization in the scorpionate ligand. These zwitterionic complexes performed as bifunctional catalysts and exhibited improved catalytic activity for the fixation of CO2 into cyclic carbonates compared to the neutral analog mononuclear [Zn(R)(κ3-NNO)] and binuclear [Zn(R)(κ2-NNµ-O)Zn(R)2] compounds. The catalyst system showed a broad substrate scope and functional group tolerance under mild and solvent-free conditions.

Synthesis of helical aluminium catalysts for cyclic carbonate formation.

Helical aluminium complexes [Al2X4(µ-nbptam)] (X = Me 1, Et 2), [Al2X4(µ-fbpam)] (R = Me 3, Et 4), [Al3X7(µ-nbptam)] (X = Me 5, Et 6) and [Al3X7(µ-fbpam)] (X = Me 7, Et 8) have been prepared by treatment of scorpionate ligand precursors with two or three equivalents of the corresponding trialkylaluminium derivative. The structures of these complexes have been determined by spectroscopic methods and the X-ray crystal structure of complex 1 has also been established. These complexes have been studied as catalysts for the chemical fixation of carbon dioxide into cyclic carbonates displaying good catalytic activity. When cyclohexene oxide was used as a substrate, polyether-polycarbonate was obtained in a ratio which is highly dependent on the cocatalyst and the catalyst to cocatalyst ratio used.

Influence of the Counterion on the Synthesis of Cyclic Carbonates Catalyzed by Bifunctional Aluminum Complexes.

New bifunctional aluminum complexes have been prepared with the aim of studying the effect of a counterion on the synthesis of cyclic carbonates from epoxides and carbon dioxide (CO2). Neutral ligand 1 was used as a precursor to obtain four novel mesylate, chloride, bromide, and iodide zwitterionic NNO ligands (2-5). The reaction of these ligands with 1 or 2 equiv of AlR3 (R = Me, Et) allowed the synthesis of mono- and bimetallic bifunctional aluminum complexes [AlR2(κ2-mbpzappe)]X [X = Cl, R = Me (6), Et (7); X = Br, R = Me (8), Et (9); X = I, R = Me (10), Et (11)] and [{AlR2(κ2-mbpzappe)}(µ-O){AlR3}]X [X = MeSO3, R = Me (12), Et (13); X = Cl, R = Me (14), Et (15); X = Br, R = Me (16), Et (17); X = I, R = Me (18), Et (19)] via alkane elimination. These complexes were studied as catalysts for the synthesis of cyclic carbonates from epoxides and CO2. Iodide complex 11 showed to be the most active catalyst for terminal epoxides, whereas bromide complex 9 was found to be the optimal catalyst when internal epoxides were used, showing the importance of the nucleophile cocatalyst on the catalytic activity.

Organo-Aluminum and Zinc Acetamidinates: Preparation, Coordination Ability, and Ring-Opening Polymerization Processes of Cyclic Esters.

The reaction of the highly sterically demanding NNN'-heteroscorpionate protioligands pbptamd-H, tbptamd-H, and phbptamd-H (a) and the low sterically hindered analogs pbpamd-H, tbpamd-H, and phbpamd-H (b), with 1 equiv of AlR3 (R = Me, Et) proceed in high yields to give two families of complexes: the mononuclear dialkyl aluminum bidentate-acetamidinates [AlR2(κ2- N' N')] (κ2- N' N' = pbptamd, R = Me 1, Et 2; tbptamd, R = Me 3, Et 4; phbptamd, R = Me 5, Et 6) and the monodentate-acetamidinates [AlR2(κ2- NN')] (κ2- NN' = tbpamd, R = Me 7; phbpamd, R = Me 8, Et 9). In complexes 7-9, the presence of two possible CH-NH tautomers as low extended π-N-C-N'(sp2)-Al and high extended π-HN-C2-N'(sp2)-Al complexes, respectively, could be identified. Moreover, the reaction of aluminum dimethyls 7 and 8 with ZnMe2 afforded the isolation of the more stable scorpionate zinc monoalkyls [Zn(Me)(κ3- NNN')] ( NNN' = tbpamd 10 and phbpamd 11), through a very unusual ligand exchange process, involving a zinc-to-aluminum transmetalation of an alkyl group. The X-ray crystal structures of 1, 3, 7, and 8, as well as that of 11, confirmed unambiguously the different κ2-arrangements proposed for bi- or monodentate acetamidinate dialkyls 1-6 and 7-9, respectively, the presence of NH tautomer in 7 and 8, and a κ3- NNN' coordination in monoalkyl 11. Density functional theory calculations were used to explore the three different favored κ2-arrangements found in acetamidinate aluminum dialkyls 1-9, the relative stability of both CH-NH tautomers, and the ligand transfer reaction leading to the formation of κ3- NNN' zinc monoalkyls 10 and 11. Interestingly, dialkyls 1, 5, 7, and 8 can act as highly efficient single-component living initiators for the ring-opening polymerization of ε-caprolactone and rac-lactide in mild conditions after hours. These initiators efficiently mediated the immortal polymerization in the presence of excess of benzyl alcohol (up to 20 equiv), as evidenced by the narrow dispersity values and the good agreement between the experimental Mn values and monomer/benzyl alcohol ratios. In addition, the most sterically hindered initiator, 5, exhibits enhanced levels of heteroselectivity on the produced PLAs, reaching Ps values up to 0.70.

Alternating Copolymerization of Epoxides and Anhydrides Catalyzed by Aluminum Complexes.

The optimization of an organoaluminum catalytic system for the copolymerization of epoxides and anhydrides is presented. For this purpose, the influence of different variables in the process, such as catalysts, cocatalyst, solvent, or substrates, has been analyzed. Kinetic studies, a proposal for the catalytic mechanism, and full characterization of the copolymers obtained are also discussed. Finally, a new copolymer, poly(limonene succinate), obtained by the optimized catalytic system is reported.

Mono- and binuclear chiral N,N,O-scorpionate zinc alkyls as efficient initiators for the ROP of rac-lactide.

The preparation of new chiral bis(pyrazol-1-yl)methane-based N,N,O-donor scorpionate ligands in the form of the alcohol compounds bpzampeH (1) {2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[4-(dimethylamino)phenyl]ethanol}, bpzaepeH (2) {2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[4-(diethylamino)phenyl]ethanol}, and bpzimeH (3) {2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[1-methyl-1H-imidazol-2-yl]ethanol} has been carried out by the 1,2-addition reactions of a series of aldehydes. These new chiral heteroscorpionate ligands reacted with [ZnR2] (R = Me, Et, CH2SiMe3) in a 1 : 1 molar ratio in toluene to give the mononuclear monoalkyl zinc complexes [Zn(R)(κ3-NNO)] (4-12). When these reactions were carried out in a 1 : 2 molar ratio the binuclear trisalkyls [Zn(R)(κ2-NNµ-O)Zn(R)2] (13-18) were obtained. The structures of these complexes were elucidated by 1H and 13C{1H} NMR spectroscopy and the X-ray crystal structures of 4 and 5 were also established. Interestingly, alkyl-containing zinc complexes 4-13, 15 and 17 act as efficient single-component initiators for the ring-opening polymerization of rac-lactide at 20 °C to afford PLA materials with low molecular weights in a few hours. The dinuclear trisalkyls showed higher activity in comparison with the mononuclear zinc counterparts, suggesting a cooperative effect of the two remote metals. The narrow dispersity ranges (Mw/Mn = 1.05) of the isolated polymers in conjunction with the linear nature of the number average molecular weight versus conversion plot provided evidence for living behavior. Inspection of the kinetic parameters showed that the propagations have the usual pseudo-first-order dependence on rac-lactide and catalyst concentration. End-group analysis and MALDI-TOF mass spectrometry confirmed that the initiation occurs through nucleophilic attack of the alkyl on the lactide monomer. Microstructural analysis of poly(rac-lactide)s revealed that the most sterically hindered ligand on the alkoxide fragment exerts a moderate influence on the degree of stereoselectivity, with heteroenriched-PLAs (Ps = 0.68) produced at room temperature.

An Efficient and Versatile Lanthanum Heteroscorpionate Catalyst for Carbon Dioxide Fixation into Cyclic Carbonates.

A new lanthanum heteroscorpionate complex has shown exceptional catalytic activity for the synthesis of cyclic carbonates from epoxides and carbon dioxide. This catalyst system also promotes the reaction of bio-based epoxides to give an important class of bis(cyclic carbonates) that can be further used for the production of bio-derived non-isocyanate polyurethanes. The catalytic process requires low catalyst loading and mild reaction conditions for the synthesis of a wide range of cyclic carbonates.

Highly thermally stable and robust enantiopure zirconium NNN-scorpionates for the controlled ring-opening polymerization of rac-lactide.

A series of enantiopure alkoxide and thioalkoxide zirconium derivatives [Zr(ER)3(κ3-R,R-fbpza)] (1-6) (E = O, R = CHMe21, CHMeEt 2, CH2SiMe33, 2,6-C6H3Me24, 4-tBuPh 5; E = S, R = 4-tBuPh 6) has been prepared for use as thermally stable and robust initiators in the ROP of rac-lactide. The compounds were prepared by alcoholysis or thioalcoholysis of the tris(amide) precursor [Zr(NMe2)3(κ3-R,R-fbpza)] [R,R-fbpzaH = N-p-fluorophenyl-(1R)-1-[(1R)-6,6-dimethylbicyclo[3.1.1]-2-hepten-2-yl]-2,2-bis(3,5-dimethylpyrazol-1-yl)ethylamine] with ROH and ArEH (E = O, S) in a 1 : 3 molar ratio. The structures of the different compounds were determined by spectroscopic methods and, in addition, the X-ray crystal structure of 6 was also established. Interestingly, the tris(amide) precursor and complexes 2, 5, and 6 act as single-site living initiators for the well-controlled ring-opening polymerization of rac-lactide both in solution and in the melt. These processes produce polymers with medium molecular weights in good agreement with theoretical values and with narrow dispersity ranges. The activity of all initiators increased markedly with temperature and, more importantly, complex 2 exhibits the highest activity reported to date for a group 4-based initiator in the ROP of rac-LA under the industrially preferred melt and solvent-free conditions. Surprisingly, complex 2 is still highly active in the melt when using an unpurified monomer and it shows an unprecedented tolerance to water and impurities (49% conv., 15 min, 130 °C). Microstructural analysis of the poly(rac-lactide)s revealed a moderate heteroactivity in solution, with a Ps value of up to 0.70.

Catalytic behaviour in the ring-opening polymerisation of organoaluminiums supported by bulky heteroscorpionate ligands.

A series of alkyl organoaluminium complexes based on bulky heteroscorpionate ligands were designed as catalysts for the ring-opening polymerisation of cyclic esters. Thus, the treatment of AlX3 (X = Me, Et) with bulky acetamide or thioacetamide heteroscorpionate ligands nbptamH (1) [nbptamH = N-naphthyl-2,2-bis(3,5-dimethylpyrazol-1-yl)thioacetamide], fbpamH (2) [fbpamH = N-fluorenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamide], ptbptamH (3) [ptbptamH = N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide], ntbptamH (4) [ntbptamH = N-naphthyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide], ptbpamH (5) [ptbpamH = N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)acetamide] and (S)-mtbpamH (6) [(S)-mtbpamH = (S)-(−)-N-α-methylbenzyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)acetamide] for 1 hour at 0 °C afforded the dialkyl aluminium complexes [AlX2{κ(2)-nbptam}] (X = Me 7, Et 8), [AlX2{κ(2)-fbpam}] (X = Me 9, Et 10), [AlX2{κ(2)-ptbptam}] (X = Me 11, Et 12), [AlX2{κ(2)-ntbptam}] (X = Me 13, Et 14), [AlX2{κ2(-)ptbpam}] (X = Me 15, Et 16) and [AlX2{κ(2)-(S)-mtbpam}] (X = Me 17, Et 18). The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structure of 14 was also established. The alkyl-containing aluminium complexes 7­18 can act as efficient single-component initiators for the ring-opening polymerisation of ε-caprolactone and rac-lactide. The polymerisations are living, as evidenced by the narrow polydispersities of the isolated polymers and the linear nature of the number average molecular weight versus conversion plot. Finally, a comparative study of ring-opening polymerisation for new bulky heteroscorpionate aluminium initiators and the less congested aluminium analogues is reported.

Enantiopure N,N,O-scorpionate zinc amide and chloride complexes as efficient initiators for the heteroselective ROP of cyclic esters.

The reaction of bpzbeH, bpzteH (racemic mixture) or (R,R)-bpzmmH (enantiopure) with the amide complexes Zn{N(SiMe3)2}2 or Zn{N(SiHMe2)2}2 in 1 : 1 molar ratio in toluene afforded the mononuclear amide zinc complexes [Zn(NR2)(κ(3)-NNO)] (1-6) [κ(3)-NNO = bpzbe, R = SiMe3 1, SiHMe2 2; bpzte, R = SiMe3 3, SiHMe2 4; (R,R)-bpzmm, SiMe3 5, SiHMe2 6]. These complexes were employed in a protonolysis reaction with HCl-Et2O in 2 : 1 molar ratio to yield the dinuclear amide/chloride zinc complexes [Zn(κ(2)-NN-µ-O)2{ZnCl(NR2)}] (7-12) [κ(2)-NN-µ-O = bpzbe, R = SiMe3 7, SiHMe2 8; bpzte, R = SiMe3 9, SiHMe2 10; (R,R)-bpzmm, SiMe3 11, SiHMe2 12]. The mononuclear complexes 5 and 6 and dinuclear complexes 11 and 12 are the first enantiopure-scorpionate zinc amide complexes to be synthesized. The single-crystal X-ray structure analysis of derivatives 1 and 3 confirmed a monomeric 4-coordinative structure in which the heteroscorpionate ligands are in a κ(3) coordination mode, while 8 had a dimeric molecular disposition with two µ-bridging alkoxides of the heteroscorpionate ligands between the two six- and four-coordinate Zn(II) centers. Interestingly, the chiral amide-containing zinc complexes 1-5 and 11 can act as single-component initiators for the ring-opening polymerization of ε-caprolactone and lactides under mild conditions, affording, in a few hours, medium/low molecular weight polymers with low polydispersity indices. MALDI-ToF mass spectra confirmed that the initiation occurred through a nucleophilic attack by the amide on the lactide monomer, and inspection of the kinetic parameters showed that propagations present the usual pseudo-first order dependence on monomer and catalyst concentrations. In addition, microstructural analysis of poly(rac-lactide)s revealed that the myrtenal substituent on the alkoxide fragment has a significant influence on the degree of stereoselectivity, producing enriched-heterotactic PLAs with a P(s) value of up to 0.79 under mild conditions.

Synthesis and structural characterization of amido scorpionate rare earth metals complexes.

The reactivity of hybrid scorpionate/cyclopentadienyl ligands in the form of the protio derivatives as a mixture of two regioisomers, namely bpzcpH [1-{2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl}-1,3-cyclopentadiene and 2-{2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl}-1,3-cyclopentadiene] and bpztcpH [1-{2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethyl}-1,3-cyclopentadiene and 2-{2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethyl}-1,3-cyclopentadiene], with the tris(silylamide) precursors [M{N(SiHMe2)2}3(thf)x] of rare earth metals (including the group 3 metals scandium and yttrium) is related to the atomic radii of the metal centres. The reaction with the precursor containing the smallest ion, [Sc{N(SiHMe2)2}3(thf)], did not proceed even heating at reflux temperature in toluene. The reaction with the precursors that contain a medium-sized metal ion, i.e., [M{N(SiHMe2)2}3(thf)2] (M = Y, Lu), proceeded only at high temperature and gave good yields of the silylenediamide-containing derivatives [M{κ(2)-NN-Me2Si(NSiHMe2)2}(bpzcp)] (M = Y , Lu ) and [M{κ(2)-NN-Me2Si(NSiHMe2)2}(bpztcp)] (M = Y , Lu ) by an double activation of Si-H and Si-N bonds. However, the reaction with the precursors that contained the largest metal ions, i.e., [M{N(SiHMe2)2}3(thf)2] (M = Nd, Sm), proceeded rapidly at room temperature to afford the bis(silylamide) complexes [M{N(SiHMe2)2}2(bpzcp)] (M = Nd , Sm ) and [M{N(SiHMe2)2}2(bpztcp)] (M = Nd , Sm ). Additionally, the alkyl heteroscorpionate yttrium and lutetium complexes [M(CH2SiMe3)2(NNCp)] (M = Y, Lu) reacted with an excess of HN(SiHMe2)2 to give the mixed alkyl/amide derivatives [M{N(SiHMe2)2}(CH2SiMe3)(bpzcp)] (M = Y , Lu ) and [M{N(SiHMe2)2}(CH2SiMe3)(bpztcp)] (M = Y , Lu ). The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structures of , and were also established.