Georgii K. Fukin

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.

Oxidation by oxygen and sulfur of Tin(IV) derivatives containing a redox-active o-amidophenolate ligand.

Oxidation of tin(IV) o-amidophenolate complexes [Sn(ap)Ph(2)] (1) and [Sn(ap)Et(2)(thf)] (2) (ap=dianion of 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone (ImQ)) with molecular oxygen and sulfur in toluene solutions was investigated. The reaction of oxygen with 1 at room temperature forms a paramagnetic derivative [Sn(isq)(2)Ph(2)] (3) (isq=radical anion of ImQ) and diphenyltin(IV) oxide [{Ph(2)SnO}(n)]. Interaction of 1 with sulfur gives another monophenyl-substituted paramagnetic tin(IV) complex, [Sn(ap)(isq)Ph] (4), and the sulfide, [Ph(3)Sn](2)S. The oxidation of 2 with oxygen and with sulfur proceeds through the derivative [Sn(isq)(2)Et(2)] (7), which undergoes alkyl elimination to give two new tin(IV) compounds, [Sn(ap)(isq)Et] (5) and [Sn(ap)(EtImQ)Et] (6) (EtImQ=2,4-di-tert-butyl-6-(2,6-diisopropylphenylimino)-3-ethylcyclohexa-1,4-dienolate ligand), respectively, along with the corresponding alkyltin(IV) oxide and sulfide. Complexes 3-5 and 7 were studied by EPR spectroscopy. The structures of 3, 4 and 6 were investigated by X-ray analysis.

Synthesis, Structures, and Properties of Novel N‐Aryl‐phenanthren‐o‐iminoquinones

Abstract The interaction of 9,10‐phenanthrenquinone with primary amines has been studied. Use of sterically hindered anilines gave the phenanthren‐o‐iminoquinones in good yields. These compounds are structural analogues of o‐benzoquinones. Using single‐electron reduction, o‐iminoquinones may synthesize metals free‐radical complexes.

The interaction of N,N′-bis(2,6-dimethylphenyl)imidazol-2-ylidene with o-benzosemiquinonato zinc(II) and indium(III) complexes

The N-heterocyclic carbene N,N′-bis(2,6-dimethylphenyl)imidazol-2-ylidene (NHC) interacts with non-transition metal complexes bearing redox-active o-benzosemiquinonato ligands in two ways: as a neutral donor or as a reducer. The reaction of NHC with (3,6-SQ)2Zn·Et2O gives the carbene adduct (3,6-SQ)2Zn·{CN(Me2Ph)(CH)2N(Me2Ph)} (1) while reaction with (3,6-SQ)3In forms the ionic complex [(3,6-SQ)2(3,6-Cat)In]− {HCN(Me2Ph)(CH)2N(Me2Ph)}+ (2) as the main product.

Redox‐Active Ligand‐Assisted Two‐Electron Oxidative Addition to Gallium(II)

The reaction of digallane (dpp-bian)Ga-Ga(dpp-bian) (2) (dpp-bian=1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) with allyl chloride (AllCl) proceeded by a two-electron oxidative addition to afford paramagnetic complexes (dpp-bian)Ga(η1 -All)Cl (3) and (dpp-bian)(Cl)Ga-Ga(Cl)(dpp-bian) (4). Treatment of complex 4 with pyridine induced an intramolecular redox process, which resulted in the diamagnetic complex (dpp-bian)Ga(Py)Cl (5). In reaction with allyl bromide, complex 2 gave metal- and ligand-centered addition products (dpp-bian)Ga(η1 -All)Br (6) and (dpp-bian-All)(Br)Ga-Ga(Br)(dpp-bian-All) (7). The reaction of digallane 2 with Ph3 SnNCO afforded (dpp-bian)Ga(SnPh3 )2 (8) and (dpp-bian)(NCO)Ga-Ga(NCO)(dpp-bian) (9). Treatment of GaCl3 with (dpp-bian)Na in diethyl ether resulted in the formation of (dpp-bian)GaCl2 (10). Diorganylgallium derivatives (dpp-bian)GaR2 (R=Ph, 11; tBu, 14; Me, 15; Bn, 16) and (dpp-bian)Ga(η1 -All)R (R=nBu, 12; Cp, 13) were synthesized from complexes 3, 10, Bn2 GaCl, or tBu2 GaCl by salt metathesis. The salt elimination reaction between (dpp-bian)GaI2 (17) and tBuLi was accompanied by reduction of both the metal and the dpp-bian ligand, which resulted in digallane 2 as the final product. Similarly, the reaction of complex 10 with MentMgCl (Ment=menthyl) proceeded with reduction of the dpp-bian ligand to give the diamagnetic complex [(dpp-bian)GaCl2 ][Mg2 Cl3 (THF)6 ] (18). Compounds 11, 12, 13, 15, and 16 were thermally robust, whereas compound 14 decomposed when heated at reflux in toluene to give complex (dpp-bian-tBu)GatBu2 (19). Both complexes 7 and 19 contain R-substituted dpp-bian ligand: in the former compound the allyl group was attached to the imino-carbon atom, whereas in complex 19, the tBu group was situated on the naphthalene ring. Crystal structures of complexes 3, 8, 9, 10, 13, 14, 18, and 19 were determined by single-crystal X-ray analysis. The presence of dpp-bian radical anions in 3, 6, 8, and 10-16 was determined by ESR spectroscopy.

Molecular and crystalline structure of pyrocatechol and hydroquinone dimethacrylates and their reactivity in melts

X-ray diffraction analysis of pyrocatechol and hydroquinone dimethacrylates (Tm = 18 and 86–88°C, respectively) shows that the oligomer molecules within crystals are packed in stacks where the methacrylate fragments of neighboring molecules are parallel to each other. The minimum distances between the centers of double bonds of adjacent methacrylate fragments in crystals of pyrocatechol and hydroquinone dimethacrylates are 4.621(3) and 4.269(4) A. The curves showing the reduced rate of photopolymerization of oligomer melts versus conversion (9,10-phenanthrenequinone used as the initiator) display a maximum at conversions of 1.5–3.0%. The limiting conversion in photopolymerization of molten pyrocatechol dimethacrylate at 25 and 40°C is 20%; for hydroquinone dimethacrylate at 95°C, it is approximately 10%. As the temperature rises from 25 to 40°C, the maximum reduced rate of photopolymerization of pyrocatechol dimethacrylate increases by a factor of 1.4.

Molecular and crystalline structure of 2,2-di(phenyl-4-ol)propane dimethacrylate, 2,2-di(phenyl-4-ol)propane diacrylate, pyrocatechol diacrylate, and hydroquinone diacrylate: Reactivity in melts

The X-ray diffraction analysis of 2,2-di(phenyl-4-ol)propane dimethacrylate, 2,2-di(phenyl-4-ol)propane diacrylate, pyrocatechol diacrylate, and hydroquinone diacrylate has shown that oligomer molecules within crystals are packed in stacks, where (meth)acrylate fragments of neighboring molecules are parallel to each other. The minimum distances between the centers of double bonds C=C of (meth)acrylate fragments in 2,2-di(phenyl-4-ol)propane dimethacrylate, 2,2-di(phenyl-4-ol)propane diacrylate, pyrocatechol diacrylate, and hydroquinone diacrylate are 4.208, 4.012, 3.621, and 3.739 describing the reduced rate of photopolymerization of molten monomers (with 9,10-phenanthrenequinone used as a photoinitiator) versus conversion show maxima at degrees of polymerization of 8, 16, 22, and 38%; the limiting conversions are 29, 36, 44, and 86%, respectively. The maximum reduced rates of photopolymerization of 2,2-di(phenyl-4-ol)propane dimethacrylate and diacrylate are nearly the same, whereas the rates of photopolymerization of hydroquinone diacrylate and pyrocatechol diacrylate are higher by a factor of 4 than those of the corresponding dimethacrylates.

Crystal packing and reactivity of di(meth)acrylates of some derivatives of hydroquinone and pyrocatechol in melts

The X-ray diffraction study of 2,2′-(1,2-phenylene-bis(oxy)diethanol and 2,2′-(1,4-phenylenebis(oxy)diethanol dimethacrylates and 2,2′-(1,4-phenylenebis(oxy)diethanol diacrylate (T m = 40–42, 68–70, and 62–64°C, respectively) indicates that oligomer molecules are packed in crystals as stacks in which methacrylate fragments of adjacent molecules are parallel to each other. The minimum distances between the centers of C=C double bonds of adjacent methacrylate fragments in crystals of di(meth)acrylates are 4.373, 4.215, and 3.996 respectively. The conversion dependences of the reduced rates of photopolymerization of melted oligomers (9,10-phenanthrenequinone as a photoinitiator) pass through maxima at conversions of 40, 11, and 2%, while the ultimate conversions are 85, 33, and 73%, respectively. The addition of ionic liquids based on phosphonium and imidazolium cations to dimethacrylates of 2,2′-(1,2-phenylenebis(oxy)diethanol and triethylene glycol increases the maximum reduced rate of photopolymerization.