Anton V. Cherkasov

Bis(guanidinate) Alkoxide Complexes of Lanthanides : Synthesis, Structures and Use in Immortal and Stereoselective Ring-Opening Polymerization of Cyclic Esters

A series of new bis(guanidinate) alkoxide Group 3 metal complexes [Ln((Me3Si)2NC(NiPr)2)2(OR)] (R=OtBu, Ln=Y, Nd, Sm, Lu; R=OiPr, Ln=Y, Nd, Lu) has been synthesized. X-ray structural determinations revealed that bis(guanidinate) tert-butoxides are monomeric complexes. The isopropoxide complex [Y((Me3Si)2NC(NiPr)2)2(OiPr)] undergoes slow decomposition in solution, to afford the unusual dimeric amido complex [(Y((Me3Si)2NC(NiPr)2)2(mu-N(iPr)C triple chemical bond N))2]. Complexes [Ln((Me3Si)2NC(NiPr)2)2(OR)] (R=OtBu, Ln=Y, Nd, Sm, Lu; R=OiPr, Ln=Y, Nd, Lu) are active catalysts/initiators for the ROP of rac-lactide and rac-beta-butyrolactone under mild conditions. Most of those polymerizations proceed with a significant degree of control. Bis(guanidinate) alkoxides appear to be well suited for achieving immortal polymerization of lactide, through the introduction of large amounts of isopropanol as a chain-transfer agent. The synthesized complexes are able to promote the stereoselective ROP of rac-beta-butyrolactone to afford syndiotactic poly(hydrobutyrate) through a chain-end control mechanism, while they are surprisingly non-stereoselective for the ROP of lactide under strictly similar conditions.

Yttrium complexes supported by linked bis(amide) ligand: synthesis, structure, and catalytic activity in the ring-opening polymerization of cyclic esters.

A series of new yttrium complexes supported by the bulky enediamido dianionic ligand DAB(2-) (DAB(2-) = (2,6-C(6)H(3)iPr(2))NC(Me)=C(Me)N(2,6-C(6)H(3)iPr(2))(2-)), that is, {DAB}Y(THF)(2)(mu-Cl)(2)Li(THF)(2) (1), {DAB}Y(OtBu)(THF)(DME) (2), and {{DAB}Y(BH(4))(2)}{Li(DME)(3)} (3), was synthesized by salt metathesis. The complexes were isolated after recrystallization in 73, 66, and 52% yield, respectively, and characterized in solution by NMR and in the solid state by single-crystal X-ray diffraction studies. In complex 1, the DAB(2-) ligand is bonded to the metal center via two covalent YN bonds, while in complexes 2 and 3 additional eta(2)-coordination of the C=C bond to the metal atom is observed, both in solution and in the solid state. The tert-butoxide and borohydride complexes 2 and 3 act as monoinitiators for the room temperature ring-opening polymerization of racemic lactide and beta-butyrolactone, providing atactic polymers with controlled molecular weights and relatively narrow polydispersities (M(w)/M(n) = 1.15-1.82). Effectively immortal ROP of lactide with as many as 50 equiv of isopropanol per metal center was performed using complex 2 as the catalyst.

Addition of Alkynes to a Gallium Bis‐Amido Complex: Imitation of Transition‐Metal‐Based Catalytic Systems

Acetylene, phenylacetylene, and alkylbutynoates add reversibly to (dpp-bian)Ga-Ga(dpp-bian) (dpp-bian=1,2-bis[(2,6-diisopropylphenyl)-imino]acenaphthene) to give addition products [dpp-bian(R(1)C=CR(2))]Ga-Ga[(R(2)C=CR(1))dpp-bian]. The alkyne adds across the Ga-N-C section, which results in new carbon-carbon and carbon-gallium bonds. The adducts were characterized by electron absorption, IR, and (1)H NMR spectroscopy and their molecular structures have been determined by single-crystal X-ray analysis. According to the X-ray data, a change in the coordination number of gallium from three [in (dpp-bian)Ga-Ga(dpp-bian)] to four (in the adducts) results in elongation of the metal-metal bond by approximately 0.13 Å. The adducts undergo a facile alkynes elimination at elevated temperatures. The equilibrium between [dpp-bian(PhC=CH)]Ga-Ga[(HC=CPh)dpp-bian] and [(dpp-bian)Ga-Ga(dpp-bian) + 2 PhC≡CH] in toluene solution was studied by (1)H NMR spectroscopy. The equilibrium constants at various temperatures (298≤T≤323 K) were determined, from which the thermodynamic parameters for the phenylacetylene elimination were calculated (ΔG°=2.4 kJ mol(-1), ΔH°=46.0 kJ mol(-1), ΔS°=146.0 J K(-1) mol(-1)). The reactivity of (dpp-bian)Ga-Ga(dpp-bian) towards alkynes permits use as a catalyst for carbon-nitrogen and carbon-carbon bond-forming reactions. The bisgallium complex was found to be a highly effective catalyst for the hydroamination of phenylacetylene with anilines. For instance, with [(dpp-bian)Ga-Ga(dpp-bian)] (2 mol%) in benzene more than 99% conversion of PhNH(2) and PhC≡CH into PhN=C(Ph)CH(3) was achieved in 16 h at 90 °C. Under similar conditions, the reaction of 1-aminoanthracene with PhC≡CH catalyzed by (dpp-bian)Ga-Ga(dpp-bian) formed a carbon-carbon bond to afford 1-amino-2-(1-phenylvinyl)anthracene in 99% yield.

Neodymium borohydride complexes supported by diamino-bis(phenoxide) ligands : diversity of synthetic and structural chemistry, and catalytic activity in ring-opening polymerization of cyclic esters

New heterobimetallic borohydrido neodymium complexes {[OONN]1Nd(BH4)(μ-BH4)Li(THF)}2 (1) and [OONN]3Nd(BH4)(μ-BH4)Li(THF)2 (3) supported by diamino-bis(phenoxide) ligands ([OONN]1 = {CH2N(Me)CH2-3,5-Me,t-Bu-C6H2O}2; [OONN]3 = C5H4NCH2N{CH2-3,5-Me,t-Bu-C6H2O}2) were synthesized by the reactions of Nd(BH4)3(THF)2 with equimolar amounts of dilithium derivatives of diamino-bis(phenol)s Li2[OONN]n and isolated in high yields. In the case of Li2[OONN]2 ([OONN]2 = Me2NCH2CH2N{CH2-3,5-t-Bu-C6H2O}2), the same synthetic procedure afforded the heterobimetallic bis(phenoxide) complex Li{Nd[OONN2]2} (2). The structures of complexes 1–3 were established by X-ray diffraction studies. Compounds 1–3 act as single-site initiators for the ring-opening polymerization (ROP) of racemic lactide and racemic β-butyrolactone under mild conditions (20 °C), providing atactic polymers with controlled molecular weights and relatively narrow polydispersities (Mw/Mn = 1.07–1.82). While 1 and 3 initiate polymerizationvia their borohydride groups, ROP with 2 proceeds viainsertion into the Nd–O(ligand) bond.

Amido Ln(II) Complexes Coordinated by Bi- and Tridentate Amidinate Ligands: Nonconventional Coordination Modes of Amidinate Ligands and Catalytic Activity in Intermolecular Hydrophosphination of Styrenes and Tolane

Heteroleptic Ln(II) and Ca(II) amides [tBuC(NC6H3-iPr2-2,6)2]MN(SiMe3)2(THF) (M = Yb (1Yb), Ca (1Ca)), [2-MeOC6H4NC(tBu)N(C6H3-iPr2-2,6)]LnN(SiMe3)2(THF) (Ln = Sm (2Sm), Yb (2Yb)), and [2-Ph2P(O)C6H4NC(tBu)N(C6H3-Me2-2,6)]YbN(SiMe3)2(THF) (3Yb) coordinated by bi- and tridentate amidinate ligands were obtained by the amine elimination reactions of M[N(SiMe3)2](THF)2 (M = Yb, Sm, Ca) with parent amidines in good yields. Complex [tBuC(NC6H3-iPr2-2,6)2]SmN(SiMe3)2 can be obtained only by a salt metathesis reaction of [tBuC(NC6H3-2,6-iPr2)2]SmI(THF)2 with NaN(SiMe3)2. Unlike 1Yb and 1Ca in 1Sm the amidinate ligand is coordinated to metal ion in κ(1)-amido:η(6)-arene fashion preventing THF coordination. The derivatives of tridentate amidinate ligands bearing pendant donor 2-MeOC6H4 or 2-Ph2P(O)C6H4N groups feature nonconventional κ(1)-N,κ(2)-O,η(6)-arene coordination mode. Complexes 1Ca, 1Sm, 1Yb, 2Sm, 2Yb, and 3Yb proved to be efficient catalysts for styrene hydrophosphination with PhPH2 and Ph2PH. In styrene hydrophosphination with PhPH2 all the catalysts perform excellent chemoselectivity and afford a monoaddition product-secondary phosphine (PhCH2CH2)PhPH. Moreover, all the catalysts perform hydrophosphination reactions regioselectively with exclusive formation of the anti-Markovnikov addition product. Within the series of complexes coordinated by the same amidinate ligand catalytic activity decreases in the following order 1Ca ≥ 1Sm>1Yb. The turnover frequencies were in the range of TOF ≈ 0.3-0.7 h(-1). However, application of tridentate amidinate ligand allowed one to increase catalytic activity significantly: for 2Sm TOF was found to be 8.3 h(-1). For the addition of PhPH2 to para-substituted styrenes catalyzed by 2Sm it was found that electron-withdrawing substituents (Cl, F) do not affect the reaction rate while electron-donating groups (tBu, OMe) noticeably slow down the reaction.

Metal-to-Ligand Alkyl Migration Inducing Carbon–Sulfur Bond Cleavage in Dialkyl Yttrium Complexes Supported by Thiazole-Containing Amidopyridinate Ligands: Synthesis, Characterization, and Catalytic Activity in the Intramolecular Hydroamination Reaction

Neutral Y(III) dialkyl complexes supported by tridentate N(-) ,N,N monoanionic methylthiazole- or benzothiazole-amidopyridinate ligands have been prepared and completely characterized. Studies on their stability in solution revealed progressive rearrangement of the coordination sphere in the benzothiazole-containing system through an unprecedented metal-to-ligand alkyl migration and subsequent thiazole ring opening. Attempts to synthesize hydrido species from the dialkyl precursor led to the generation of a dimeric yttrium species stabilized by a trianionic N(-) ,N,N(-) ,S(-) ligand as the result of metal-to-ligand hydride migration with chemoselective thiazole ring opening and subsequent dimerization through intermolecular addition of the residual YH group to the imino fragment of a second equivalent of the ring-opened intermediate. DFT calculations were used to elucidate the thermodynamics and kinetics of the process, in support of the experimental evidence. Finally, all isolated yttrium complexes, especially their cationic forms prepared by activation with the Lewis acid Ph3 C(+) [B(C6 F5 )4 ](-) , were found to be good candidate catalysts for intramolecular hydroamination/cyclization reactions. Their catalytic performance with a number of primary and secondary amino alkenes was assessed.

Rare-earth dichloro and bis(alkyl) complexes supported by bulky amido-imino ligand. Synthesis, structure, reactivity and catalytic activity in isoprene polymerization

A monoanionic amido-imino ligand system [(2,6-iPr2C6H3)N=C(Me)C(=CH2)N(C6H3-2,6-iPr2)](-) was successfully employed for the synthesis of monomeric dichloro [(2,6-iPr2C6H3)N=C(Me)C(=CH2)N(C6H3-2,6-iPr2)]LnCl2(THF)2 (Ln = Y, 2Y; Lu, 2Lu) and bis(alkyl) [(2,6-iPr2C6H3)N=C(Me)C(=CH2)N(C6H3-2,6-iPr2)]Ln(CH2SiMe3)2(THF) (Ln = Y, 4Y; Lu, 4Lu) species of yttrium and lutetium. Dichloro complexes 2Y and 2Lu turned out to be unstable in aromatic solvents. The ligand symmetrization reaction in the case of 2Y affords the yttrium complex coordinated by dianionic [(2,6-iPr2C6H3)NC(=CH2)C(=CH2)N(C6H3-2,6-iPr2)](2-) ligand, (2,6-iPr2C6H3)N=C(Me)C(Me)=N(C6H3-2,6-iPr2) and YCl3. On the contrary, bis(alkyl) species 4Y and 4Lu are rather stable and do not undergo such a transformation or thermal decomposition. The treatment of complex 4Y with DME resulted in C-O bond cleavage and the formation of a dimeric methoxy-alkyl species {[(2,6-iPr2C6H3)N=C(Me)C(=CH2)N(C6H3-2,6-iPr2)]Y(CH2SiMe3)(μ-OMe)}2 (5). The ternary systems 4Ln/AliBu3/borate (borate = [HNMe2Ph][B(C6F5)4] and [CPh3][B(C6F5)4]; molar ratio 1 : 10 : 1) performed high catalytic activity in isoprene polymerization and ability to convert into polymer 1000-5000 equivalents of isoprene in 20-120 min with quantitative conversion. The obtained polyisoprenes possessed high molecular weights (2.9 × 10(4)-4.1 × 10(4)) and moderate polydispersities (2.14-3.52). Predominant 3,4-regioselectivity (up to 78%) was observed.

Lithium, zinc and scandium complexes of phosphorylated salicylaldimines: synthesis, structure, thermochemical and photophysical properties, and application in OLEDs

The reaction of phosphorylated salicylaldimines containing the PO group either directly attached to the central benzene core (1a) or connected with it via a methylene unit (1b) with lithium and scandium hexamethyldisilazides readily afforded [κ3-O,N,O-(L–H)Li]2 (2a,b) and [κ2-O,N-(L–H)3Sc] (3a,b) (L – ligand) complexes in high yields. The treatment of 1b with Et2Zn in the presence of 1,10-phenanthroline led to zinc(II) complex 4b of (L–H)2Zn(phen) composition featuring a bidentate coordination mode of both salicylaldiminate ligands without participation of the phosphoryl groups. The structures of the complexes obtained were confirmed by the IR spectroscopic data and, in some cases, X-ray diffraction analysis. The thermal behavior of compounds 1a,b and 4b was studied by DSC. The temperature dependences of saturated vapor pressures of ligands 1a,b and complexes 2a, 4b were measured by the Knudsen effusion method. The thermodynamic parameters characterizing crystal-to-gas phase transitions were calculated. The complexes obtained were shown to possess weak photoluminescence in THF solution at room temperature. The unoptimized three-layer OLEDs based on 2a,b and 3a,b emit green light of low and moderate intensity.

The reactivity of o-amidophenolate indium(III) complexes towards different oxidants

The reactivity of o-amidophenolate indium(III) complexes towards different oxidants was investigated. The oxidation reactions were found to proceed through the stage of paramagnetic o-iminobenzosemiquinonato indium(III) derivative formation. The monoradical intermediates undergo symmetrization. The final products of the oxidation processes are corresponding biradical o-iminobenzosemiquinonato indium(III) complexes. In order to understand the reasons for the symmetrization processes steric factors (G-parameters) were evaluated for all intermediates and final products by a method based on the ligand solid angle approach.

New type of coordination of phosphorus to carbene analogs. p(π)-Complex of 3a,6a-diaza-1,4-diphosphapentalene with germanium dichloride

Abstract3a,6a-Diaza-1,4-diphosphapentalene (1), as a neutral ligand, displays a new type of complexation, such that the lone pair at the phosphorus atom is not involved in the coordination; instead, the 10π-electron system provides two electrons for the coordination bond formation between the phosphorus atom and the metal. The p(π)-type complex–a molecular adduct of 1 with germanium dichloride — was synthesized and completely characterized. This complex is a coordination polymer with short intermolecular Ge—Ge, Ge—P, P—P, P—Cl, and Ge—C contacts.