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A series of bis(tetramethylaluminate) lanthanide complexes {2-[Ph2P═X]C6H4NC(tBu)N(2,6-Me2C6H3)}Ln(AlMe4)2 (X = O, Ln = La (1); X = O, Ln = Nd (2); X = O, Ln = Sm (3); X = S, Ln = La (4); X = S, Ln...

The isolable bis(tetramethylaluminate) lanthanide complexes [2-R2,6-XC6H4NC(tBu)(2,6-R12C6H3)]Ln(AlMe4)2 (R1 = R2 = X = Me, Ln = La (1); R1 = R2 = X = Me, Ln = Nd (2); R1 = iPr, R2 = H, X = OMe, Ln...

This study reports four SMMs based on silanolate or stannanolate ligands cis-[Dy(OSiPh3)2(THF)4][BPh4]·THF·C6H6 (1), cis-[Dy(OSnPh3)2(THF)4][BPh4]·THF·C6H6·C6H14 (2), fac-[Dy(OSiPh3)3(THF)3]·THF (3) and fac-[Dy(OSiPh3)3(bipy)(THF)]·THF (4).

We report the synthesis and structures of three luminescent dysprosium(iii) complexes based on fluorinated alkoxide ligands of formulas [Dy(L1)2(THF)4][BPh4]·0.5THF (1), [Dy(L2)2(THF)5][BPh4]·2.5THF (2) and [Dy(L3)2(THF)5][BPh4]·2THF (3) (L1 = (CF3)3CO-, L2 = C6F5C6F4O-, L3 = C6F5C(CH3)O-). Despite the different dysprosium ion geometries (octahedral vs. distorted pentagonal bipyramidal), these systems exhibit a single-molecule magnet (SMM) behavior, but with distinct relaxation dynamics. Moreover, a typical dysprosium-based luminescence is observed for the three complexes, which make them bifunctional magneto-luminescent SMMs. Remarkably, complex 3 exhibits a high anisotropy barrier of 1469 cm-1 and a blocking temperature of 22 K, making it one of the most performant alkoxide-based SMMs with the highest blocking temperature for a luminescent SMM.

The reaction of tridentate amidine 2-[Ph2P(O)]C6H4NHC(But)=N(2,6-Me2C6H3) (1) containing the side-chain donor group Ph2P=O with NdCl[N(SiMe3)2]2 (2) in a molar ratio of2:1 afforded the neodymium bis(amidinate) monochloride complex {2-[Ph2P(O)]-C6H4NC(But)N(2,6-Me2C6H3)}2NdCl (3). The neodymium bis(amidinate) monoallyl complex {2-[Ph2P(O)]C6H4NC(But)N(2,6-Me2C6H3)}2Nd(C3H5) (5) was synthesized by the elimination reaction between the tris-allyl derivative Nd(C3H5)3-(C4H8O2)2 (4) and amidine 1 in a molar ratio of 1:2 and by the exchange reaction between equimolar amounts of complex 3 and allylmagnesium bromide (C3H5MgBr). Complex 5 exhibits high activity as an initiator for the ring-opening polymerization of rac-lactide and e-caprolactone, providing the conversion of up to 500 equivalents of the rac-lactide and e-caprolactone within 5 and 2 min, respectively. The resulting polylactide samples have high number-average molecular weights ((47.38–93.02) · 103) and low polydispersity indices (Mw/Mn = 1.18–1.47). The polycaprolactone samples are characterized by high number-average molecular weights ((114.34–237.46) · 103) and a somewhat broadened molecular weight distribution (Mw/Mn = 1.87–2.40).

The reaction of 2,6-diisopropylaniline with m-phenylenedibenzimidoyl chloride 1,3-C6H4{N=C(Ph)Cl}2 in the presence of triethylamine in a toluene solution affords bis(amidine) 1,3-C6H4{NC(Ph)NH(2,6-iso-Pr2C6H3)}2 (H2L) in which two amidinate fragments are bound by the conformationally rigid m-phenylene linker. The metallation of bis(amidine) by n-butyllithium in the presence of tetramethylethylenediamine (TMEDA) occurs readily in a tetrahydrofuran solution at –70°С to form the corresponding lithium amidinate complex 1,3-C6H4{NC(Ph)N(2,6-iso-Pr2C6H3)}2Li2(TMEDA)2 (I). The X-ray structure analysis shows that complex I is monomeric (CIF file CCDC no. 1873201). Each amidinate fragment NCN is bound to one lithium atom via the κ2-N,N chelating mode.

International audience; We report the synthesis, structure and magnetic properties' investigations of a series of new dysprosium heteroleptic mono-and dinuclear complexes based on the association of chloride and different diazabutadiene (DAD 2R = [2,6-iPr2C6H3N-CRCR-NC6H3iPr2-2,6]; R = H, Me) ligands showing different redox states. While using dianionic DAD 2R ligands affords the formation of dichloro-bridged dinuclear complexes [Dy2(DAD 2R)(-Cl)2(THF)2] (R = H (1), Me (2)), two different mononuclear complexes of general formula [DyCl2(DAD 2R)(THF)2] (R = H (3), Me (4)) could be obtained with either a radical monoanionic and a monoanionic DAD 2R state, respectively. Remarkably, all the complexes exhibit a slow relaxation of their magnetization where the relaxation dynamics depends on both, the nuclearity of the system and the DAD 2R redox state.

International audience; We report in this communication the synthesis, structure and magnetic investigations of two new half-sandwich complexes [Dy(DAD)Cp*(THF)] (1) and [Li(THF) 3 ][Dy(DAD)Cp*Cl] (2) (Cp* = C 5 Me 5 , DAD = [2,6-iPr 2 C 6 H 3 N-CMeCMe-NC 6 H 3 iPr2-2,6). Both compounds exhibit zero-field SMM behavior but distinct relaxation dynamics originating from difference in the arrangement of Cp* and DAD ligands. The anisotropic barrier for 1 is found one order of magnitude greater than for 2.

The deprotonation of amidine 2-[Ph2P(O)]C6H4NHC(But)=N(2,6-Me2C6H3) (1) with BunLi affords lithium amidinate {2-[Ph2P(O)]C6H4NLiC(But)=N(2,6-Me2C6H3)}2 (2) having a dimeric structure, as demonstrated by X-ray diffraction. New amidinate dihalide complexes {2-[Ph2P(O)]C6H4NC(But)N(2,6-Me2C6H3)}NdHal2(THF)2 (Hal = I (3), Cl (4)) were synthesized by exchange reactions of lithium and potassium amidinates with anhydrous neodymium halides NdHal3(THF)n (Hal = I, n = 3.5; Cl, n = 0). The X-ray diffraction studies showed that the new compounds are monomeric and the amidinate ligand is tridentate. Chloride complex 4 involved in the three- and four-component catalyst systems 4–AlR3–[Ph3C] [B(C6F5)4] (1: 10: 1; AlR3 = AlBui 3, AlMe3), 4–AlR3–PriOH (1: 10: 10; AlR3 = AlBui3, AlMe3), and 4–AlR3–[Ph3C][B(C6F5)4]–PriOH (1: 10: 1: 10; AlR3 = AlBui3, AlMe3) exhibits activity in stereospecific isoprene polymerization and allows the preparation of high-molecular-weight polyisoprene samples with exceptionally high cis-1,4-unit content (up to 99.4%).

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 AlBu 3 i (1: 1: 10 molar ratio) exhibit catalytic activity in isoprene polymerization.

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.

A series of new tridentate amidines 2-[Ph2PX]C6H4NHC(tBu)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 Ph2PX groups in a pendant chain was synthesized. Bis(alkyl) complexes {2-[Ph2PX]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 PX (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 Ph2PO group by Ph2PNPh 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 Ph2PNPh fragment allows us to restore the 1,4-cis stereoselectivity of the catalytic systems based on bis(alkyl) complex 10 (up to 86.4%).

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—AlBui 3—[Ph3C][B(C6F5)4] (1: 10: 1 molar ratio) catalyzes the isoprene polymerization.

The salt-metathesis reactions of anhydrous LnCl3 (Ln = Y, Er) with [1,3-C6H4{NC(Ph)NSiMe3}2Li2(thf)2]2 (1; thf = tetrahydrofuran) in a 2:1 molar ratio in thf afford tris(amidinate) complexes [(1,3-C6H4{NC(Ph)NSiMe3}2)3Y(thf)Y(µ-Cl)Li(thf)3] (3) and [(1,3-C6H4{NC(Ph)NSiMe3}2)3Er2(µ-Cl)Li(thf)3] (4), which feature bridging coordination of the amidinate ligands to two Ln3+ ions. The reactions of the dilithium derivative of the related bis(amidine) with a 2,6-pyridinediyl linker, [2,6-C5H3N{NC(tBu)N(2,6-Me2C6H3)}2]2–, with LnCl3 (Ln = Y, Er) result in the formation of mononuclear chlorido bis(ligand) ate complexes [{(2,6-C5H3N)(NC{tBu}N{2,6-Me2C6H3})2}({2,6-C5H3N}{NC(tBu)N(2,6-Me2C6H3)}{NC(tBu)NH(2,6-Me2C6H3)})LnCl][Li(dme)3] [Ln = Y (5), Er (6); dme = 1,2-dimethoxyethane]. The Ln3+ ions in these complexes are coordinated by one dianionic tridentate amidopyridinate–amidinate ligand, and the second ligand is a monoanionic amidopyridinate. The reaction of YbCl3 with [(Me2Si{NC(Ph)N(2,6-iPr2C6H3)}2)2Li3][Li(thf)4], which contains a short SiMe2 linker, in a 2:1 molar ratio in thf afforded the bis(amidinate)chloridoytterbium complex [(Me2Si{NC(Ph)N(2,6-iPr2C6H3)}2)2(Yb2Cl)(µ-Cl)2Li(thf)3] (8). The magnetic properties of 4 were investigated through superconducting quantum interference device (SQUID) magnetometry.

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.

Reaction of bisamidine C6H4-1,2-{NC(t-Bu)NH(2,6-Me2C6H3)}2 (1) and [(Me3Si)2N]2Yb(THF)2 (THF = tetrahydrofuran) (toluene; room temperature) in a 1:1 molar ratio afforded a bis(amidinate) Yb(II) complex [C6H4-1,2-{NC(t-Bu)N(2,6-Me2C6H3)}2]Yb(THF) (2) in 65% yield. Complex 2 features unusual κ(1)amide, η(6)-arene coordination of both amidinate fragments to the ytterbium ion, resulting in the formation of a bent bis(arene) structure. Oxidation of 2 by Ph3SnCl (1:1 molar ratio) or (PhCH2S)2 (1:0.5) leads to the Yb(III) species [C6H4-1,2-{NC(t-Bu)N(2,6-Me2C6H3)}2]YbCl(1,2-dimethoxyethane) (3) and {[C6H4-1,2-{NC(t-Bu)N(2,6-Me2C6H3)}2]Yb(μ-SCH2Ph)}2 (4), performing "classic" κ(2)N,N'-chelating coordination mode of ansa bis(amidinate) ligand. By the reduction of 3 with equimolar amount of sodium naphthalide [C10H8(•-)][Na(+)] in THF, complex 2 can be recovered and restored to a bent bis(arene) structure. Complex 3 was also synthesized by the salt metathesis reaction of equimolar amounts of YbCl3 and the dilithium derivative of 1 in THF.

A series of lanthanide monoborohydrido complexes {C6H4-1,2-[NC(R)NR′]2}Ln(BH4)(L)n (Ln = Y, Nd, Sm; R = tBu, Ph; R′ = 2,6-Me2C6H3, SiMe3; L = dme = dimethoxyethane, n = 1; L = thf, n = 2), in which lanthanides are coordinated by bulky ansa-bis(amidinato) ligand systems with a conformationally rigid o-phenylene linker ({C6H4-1,2-[NC(R)NR′]2}2–), were synthesized by the salt metathesis reactions of equimolar amounts of Ln(BH4)3(thf)3 and {C6H4-1,2-[NC(R)NR′]2}X2(thf)n (X = Li, Na) in thf. X-ray diffraction studies revealed that the complexes are monomeric. Depending on the denticity of the donor ligand (L = dme or thf), the terminal borohydrido ligand coordinated to the metal ion can be located in either an equatorial (L = thf) or an apical (L = dme) position. All complexes are efficient catalysts for the ring-opening polymerization of rac-lactide, which allows to convert up to 1000 equiv. of monomer into a polymer at room temperature within 10–150 min and affords atactic polylactides with high molecular weights and moderate molecular-weight distributions (1.28–2.16). Yttrium–borohydrido complexes coordinated by the {C6H4-1,2-[NC(tBu)N(2,6-Me2C6H3)]2}2– ligand system showed enhanced catalytic activity compared to that of the analogue complexes containing the {C6H4-1,2-[NC(Ph)NSiMe3]2}2– ligand. The obtained borohydrido complexes catalyze the hydrophosphonylation of benzaldehyde at room temperature with good reaction rates.

Bis-amido TiIV and ZrIV complexes stabilized by ansa bis(amidinate) ligands {C6H4-1,2-[NC(tBu)N(2,6-R2C6H3)]2?M(NMe2)2 [M = ZrIV, R = Me (3), R = iPr (4); M = TiIV, R = Me (5), R = iPr (6)] and ?C6H4-1,2-[NC(tBu)N(2,6-Me2C6H3)]2}Zr(NMe2)3H (3?HNMe2) were prepared in fairly good yields by reacting a (bis)amidine ligand [C6H4-1,2-{NC(tBu)N(2,6-R2C6H3)H}2 [R = Me (1), iPr (2)] with an equimolar amount of the metal precursor [M(NMe2)4 (M = ZrIV, TiIV)]. The salt metathesis reaction between an equimolar amount of sodium amidinates ?C6H4-1,2-[NC(tBu)N(2,6-R2C6H3)]2Na2? and ZrCl4(thf)2 was also scrutinized to synthesize the corresponding ZrIV bis(amidinate) dichlorides ?C6H4-1,2-[NC(tBu)N(2,6-R2C6H3)]2?ZrCl2 [R = Me (7), iPr (8)]. The ligands coordination mode to MIV ions was found to be strongly affected by the steric hindrance of the amidinate ligands (Me vs. iPr substituted aniline moieties) as well as by the nature of the ancillary groups bound to the metal center (NMe2 vs. Cl). Bis(amido) ligands with the 2,6-Me2C6H3 substituents at the amidinate nitrogens coordinate the zirconium ion in a tetradentate fashion both in solution and in the solid state (3 and 3?HNMe2). Compounds containing the bulkier 2,6-iPr2C6H3 units prefer a tridentate coordination mode (4). With the smaller TiIV ion, all the bis(amidinate) ligands from this series are tridentate in the solid state (compounds 5 and 6) while they reversibly switch their denticity from tridentate to tetradentate (?3 vs. ?4) in solution depending on the temperature. The ZrIV complex 4, featuring with the bulkier bis(amidinate) ligand 2, shows a similar behavior to that of its TiIV analogue, with a tridentate ligand coordination at the solid state and a temperature induced denticity change in solution as a temperature function. Thermodynamic standard parameters for the ?3 vs. ?4 interconversion on the two model compounds 4 and 5 in toluene-d8 solution have been measured from the respective linear van't Hoff plots fitting. Finally, ZrIVbis(chloride) complexes 7 and 8 invariably show a tetracoordination mode of their bis(amidinate) ligands (1 and 2) both in solution and in the solid state.

ansa-Bis(amidinate) ligands with a rigid o-phenylene linker, C6H4-1,2-{NC(tBu)N(2,6-R2C6H3)H}2 (R = Me (1), iPr (2)), were successfully employed for the synthesis of rare-earth chloro and alkyl species. The reaction of dilithium derivatives of 1 and 2 with LnCl3 (Ln = Y, Lu) afforded the monomeric bis(amidinate) chloro lanthanide complexes [C6H4-1,2-{NC(tBu)N(2,6-R2C6H3)}2]Y(THF)(μ-Cl)2Li(THF)2 (R = Me (3), iPr (5)) and [C6H4-1,2-{NC(tBu)N(2,6-Me2C6H3)}2]LuCl(THF)2 (4). Bis(amidinate) ligands in complexes 3 and 4 are coordinated to the metal atoms in a tetradentate fashion, while the bulkier ligand in 5 is tridentate. The alkane elimination reactions of 1 and 2 with equimolar amounts of (Me3SiCH2)3Ln(THF)2 (Ln = Y, Lu) allowed us to obtain the monoalkyl complexes [C6H4-1,2-{NC(tBu)N(2,6-R2C6H3)}2]Ln(CH2SiMe3)(THF)n (Ln = Y, R = Me, n = 1 (6); Ln = Lu, R = Me, n = 1 (7); Ln = Y, R = iPr, n = 2 (8)). The kinetics of thermal decomposition of complexes 6–8 were measured, and for 6 the activation energy was ob...

A new tridentate amidine 2-[Ph2P(O)]C6H4NHC(tBu)[double bond, length as m-dash]N(2,6-Me2C6H3) (1) bearing a side chain pendant Ph2P[double bond, length as m-dash]O group was synthesized and proved to be a suitable ligand for coordination to rare-earths ions. Bis(alkyl) complexes {2-[Ph2P(O)]C6H4NC(tBu)N(2,6-Me2C6H3)}Ln(CH2SiMe3)2(THF)n (Ln = Y, n = 1 (3), Ln = Er, n = 1 (4), Ln = Lu, n = 0 (5)) were prepared using alkane elimination reactions of and Ln(CH2SiMe3)3(THF)2 (Ln = Y, Er, Lu) in hexane and were isolated in 50, 70 and 75% yields respectively. The X-ray studies revealed that complexes 2-5 feature intramolecular coordination of P[double bond, length as m-dash]O groups to metal ions. The lutetium complex 5 proved to be rather stable: at 20 °C its half-life time is 1155 h, while for the yttrium analogue the half-life time was found to be 63 h. Complexes 3-5 were evaluated as precatalysts for isoprene polymerization. The systems Ln/borate/AliBu3 (Ln = 3-5, borate = [PhNHMe2][B(C6F5)4], [Ph3C][B(C6F5)4]) turned out to be highly efficient in isoprene polymerization and enable complete conversion of 1000-10,000 equivalents of monomer into polymer at 20 °C within 0.5-2.5 h affording polyisoprenes with a very high content of 1,4-cis units (up to 96.6%) and from narrow (1.49) to moderate (3.54) polydispersities. A comparative study of catalytic performance of the related bis(alkyl) yttrium complexes supported by amidinate ligands of different denticities and structures [tBuC(N-2,6iPr2C6H4)2](-), [tBuC(N-2,6-iPr2C6H4)(N-2-MeOC6H4)](-) and {2-[Ph2P(O)]C6H4NC(tBu)N(2,6-Me2C6H3)}(-) demonstrated that the introduction of a pendant donor group (2-MeOC6H4 or Ph2P(O)) into a side chain of amidinate scaffolds results in a significant increase in catalytic activity. The amidinate ligand bearing a Ph2P(O)-group provides a high isoprene polymerization rate along with excellent control over regio- and stereoselectivities and allows us to obtain polyisoprenes with a reasonable molecular weight distribution.