Aleksei O. Tolpygin

Bis(amido) rare-earth complexes coordinated by tridentate amidinate ligand: synthesis, structure and catalytic activity in the polymerization of isoprene and rac-lactide

A series of bis(amido) complexes of rare earth metals {2-[Ph2P(O)]C6H4NC(tBu)N(2,6-Me2C6H3)}Ln(N(SiMe3)2)2, (Ln = Y (2), Nd (3), La (4)) was synthesized using the amine elimination reaction of Ln[N(SiMe3)2]3 (Ln = Y, Nd, La) and parent amidine 1 in THF, and the products were isolated in 60 (2), 61 (3) and 72% (4) yields, respectively. The X-ray studies revealed that complexes 2–4 are solvent-free and feature intramolecular coordination of the Ph2PO group to the Ln ion. Complexes 2–4 were investigated as precatalysts for isoprene polymerization. The ternary systems 2–4/borate/AlR3 (AlR3 = AliBu3, AliBu2H; borate = [Ph3C][B(C6F5)4], [PhNHMe2][B(C6F5)4]) were found to be active in isoprene polymerization and enable complete conversion of 1000 equivalents of monomer into polymer at 25 °C within 1–24 h affording polyisoprenes with polydispersities Mw/Mn = 1.12–9.46. The effect of the organoaluminium component and [Ln]/[AlR3] ratio on the catalytic activity and selectivity of the ternary catalytic systems was investigated. Complexes 2–4 proved to be efficient catalysts for the ring-opening polymerization of rac-lactide, which allow conversion of up to 500 equivalents of monomer into a polymer at room temperature within 30 min and afford atactic polylactides with high molecular weights and moderate molecular-weight distributions (1.29–2.12). Complexes 2–4 appear to be well-suited for achieving immortal polymerization of lactide, through the introduction of large amounts of isopropanol as a chain-transfer agent.

Bis(alkyl) rare-earth complexes coordinated by bulky tridentate amidinate ligands bearing pendant Ph2PO and Ph2PNR groups. Synthesis, structures and catalytic activity in stereospecific isoprene polymerization

A series of new tridentate amidines 2-[Ph2P[double bond, length as m-dash]X]C6H4NHC(tBu)[double bond, length as m-dash]N(2,6-R2C6H3) (X = O, R = iPr (1); X = S, R = Me (2); X = NPh, R = Me (3); X = N(2,6-Me2C6H3), R = Me (4)) bearing various types of donor Ph2P[double bond, length as m-dash]X groups in a pendant chain was synthesized. Bis(alkyl) complexes {2-[Ph2P[double bond, length as m-dash]X]C6H4NC(tBu)N(2,6-R2C6H3)}Ln(CH2SiMe3)2 (Ln = Y, X = O, R = iPr (5); Ln = Er, X = O, R = iPr (6); Ln = Lu, X = O, R = iPr (7); Ln = Y, X = NPh, R = Me (8); Ln = Lu, X = NPh, R = Me (9); Ln = Lu, X = N(2,6-Me2C6H3), R = Me (10)) were prepared using alkane elimination reactions of 1, 3 and 4 with Ln(CH2SiMe3)3(THF)2 (Ln = Y, Er, Lu) in toluene and were isolated in 45 (5), 62 (6), 56 (7), 65 (8), 60 (9), and 60 (10) % yields respectively. The X-ray diffraction studies showed that complexes 6-8 are solvent free and feature intramolecular coordination of the P[double bond, length as m-dash]X (X = O, NPh) group to the lanthanide ions. The ternary systems 5-10/borate/AlR3 (borate = [PhNHMe2][B(C6F5)4], [Ph3C][B(C6F5)4], AlR3 = AliBu3, AliBu2H; molar ratio = 1/1/10 or 1/1/1, toluene) proved to be active in isoprene polymerization and enable complete conversion of 1000-10 000 equivalents of the monomer into a polymer at 25 °C within 0.5-24 h affording polyisoprenes with polydispersities Mw/Mn = 1.22-3.18. A comparative study of the catalytic performance of the bis(alkyl) complexes coordinated by tridentate amidinate ligands containing different pendant donor groups demonstrated that replacement of the Ph2P[double bond, length as m-dash]O group by Ph2P[double bond, length as m-dash]NPh leads to a switch of stereoselectivity in isoprene polymerization from cis-1,4 (up to 98.5%) to trans-1,4 (up to 84.8%). And conversely introduction of methyl substituents in the 2,6 positions of the phenyl group of the Ph2P[double bond, length as m-dash]NPh fragment allows us to restore the 1,4-cis stereoselectivity of the catalytic systems based on bis(alkyl) complex 10 (up to 86.4%).

Synthesis, structure, and properties of rare earth chloride complexes {[Ap´Y(THF)](μ2-Cl)2(μ3-Cl)Li(THF)}2, {[Ap9MeLn(THF)](μ2-Cl)3Li(THF)2}2 (Ln = Y, Nd, Sm), and {[Ap*Ln(THF)](μ2-Cl)3Li(THF)2}2 (Ln = Nd, Sm) containing amidopyridinate ligands

New amidopyridinate chloride complexes {[Ap´Y(THF)](μ2-Cl)2(μ3-Cl)Li(THF)}2, {[Ap9MeLn(THF)](μ2-Cl)3Li(THF)2}2 (Ln = Y, Nd, Sm), and {[Ap*Ln(THF)](μ2-Cl)3Li(THF)2}2 (Ln = Nd, Sm) were synthesized by the exchange reactions of lithium amidopyridinates ApLi(OEt2) (Ap´ is N-(2,6-diisopropylphenyl)-6-(2,6-dimethylphenyl)pyridine-2-amine; Ap9Me is N-mesityl-6-(2,4,6-triisopropylphenyl)pyridine-2-amine; Ap* is N-(2,6-diisopropylphenyl)-6-(2,4,6-triisopropylphenyl)pyridine-2-amine) with anhydrous rare earth chlorides. The X-ray diffraction study showed that the amidopyridinate chloride derivatives are heterobimetallic ate-complexes, in which two rare earth metal atoms are linked by bridging chloride ligands and bridging Cl—Li—Cl groups. The three-component system {[Ap*Nd(THF)](μ2-Cl)3Li(THF)2}2—AlBui3—[Ph3C][B(C6F5)4] (1: 10: 1 molar ratio) catalyzes the isoprene polymerization.

Yttrium and ytterbium(III) complexes with ansa-linked bis(amidinate) ligand containing conformationally rigid o-phenylene bridge

The new tert-butoxide yttrium complex [C6H4-1,2-NC(But)N(2,6-Me2C6H3)}2]YOBut(DME) containing the dianionic ansa-linked bis(amidinate) ligand with the rigid o-phenylene linker was synthesized by the metathesis of the chloride complex [C6H4-1,2-NC(But)N(2,6-Me2C6H3)}2]Y(THF)(μ2-Cl)2Li(THF)2 with potassium tert-butoxide and structurally characterized. The synthesized yttrium bis(amidinate) tert-butoxide complex exhibits a moderate catalytic activity in the polymerization of rac-lactide under mild conditions but makes it possible to carry out the process with high control and obtain atactic polylactide with a narrow molecular weight distribution (Mn/Mw = 1.55) and good correspondence of the calculated and experimentally determined Mn. It was found by X-ray diffraction analysis that the substitution in the coordination sphere of the ytterbium atom in complex [C6H4-1,2-{NC(But)N(2,6-Me2C6H3)}2]YbCl(DME) of a DME molecule for two THF molecules resulted in the migration of the chloride ligand from the apical to equatorial position.

Amidinate bisborohydride complexes of rare-earth metals [6-Me-C5H3N-2-CH2C(NPri)2]Ln(BH4)2THF2 (Ln = Y, Nd): synthesis, structure, and catalytic activity in isoprene polymerization

Reactions of equimolar amounts of RN=C=NR (R = Pri, Cy) and 6-Me-C5H3N-2-CH2Li prepared in situ by metallation of 2,6-dimethylpyridine with n-butyllithium afforded corresponding lithium amidinates [Li{6-Me-C5H3N-2-CH2C(NPri)2}]•1/3THF (1) and [Li{6-MeC5H3N-2-CH2C(NCy)2}]4 (2) containing new tridentate amidinate ligands. The salt metathesis reactions of Ln(BH4)3(THF)3 (Ln = Y, Nd) with 1 (1: 1 molar ratio, THF) result in neutral amidinate bisborohydride complexes [Ln{6-Me-C5H3N-2-CH2C(NPri)2}(BH4)2(THF)2} (Ln = Y (3), Nd (4)). According to X-ray data, both compounds are monomeric, terminal borohydride ligands being coordinated to the rare earth metal atom in η3-fashion. Nitrogen atoms of the pyridine fragments of amidinate ligands are not involved in complexation with metal cations. Complexes 3 and 4 in combination with [Ph3C][B(C6F5)4] and AlBu3i (1: 1: 10 molar ratio) exhibit catalytic activity in isoprene polymerization.

CCDC 1537909: Experimental Crystal Structure Determination

Related Article: Grigorii G. Skvortsov, Aleksei O. Tolpygin, Georgy K. Fukin, Jerome Long, Joulia Larionova, Anton V. Cherkasov, Alexander A. Trifonov|2017|Eur.J.Inorg.Chem.||4275|doi:10.1002/ejic.201700639

CCDC 1537908: Experimental Crystal Structure Determination

Related Article: Grigorii G. Skvortsov, Aleksei O. Tolpygin, Georgy K. Fukin, Jerome Long, Joulia Larionova, Anton V. Cherkasov, Alexander A. Trifonov|2017|Eur.J.Inorg.Chem.||4275|doi:10.1002/ejic.201700639

CCDC 1537910: Experimental Crystal Structure Determination

Related Article: Grigorii G. Skvortsov, Aleksei O. Tolpygin, Georgy K. Fukin, Jerome Long, Joulia Larionova, Anton V. Cherkasov, Alexander A. Trifonov|2017|Eur.J.Inorg.Chem.||4275|doi:10.1002/ejic.201700639