Triphenylantimony(V) Catecholates of the Type (3-RS-4,6-DBCat)SbPh3-Catechol Thioether Derivatives: Structure, Electrochemical Properties, and Antiradical Activity

A new series of triphenylantimony(V) 3-alkylthio/arylthio-substituted 4,6-di-tert-butylcatecholates of the type (3-RS-4,6-DBCat)SbPh3, where R = n-butyl (1), n-hexyl (2), n-octyl (3), cyclopentyl (4), cyclohexyl (5), benzyl (6), phenyl (7), and naphthyl-2 (8), were synthesized from the corresponding catechol thioethers and Ph3SbBr2 in the presence of a base. The crystal structures of 1, 2, 3, and 5 were determined by single-crystal X-ray analysis. The coordination polyhedron of 1–3 is better described as a tetragonal pyramid with a different degree of distortion, while that for 5- was a distorted trigonal bipyramid (τ = 0.014, 0.177, 0.26, 0.56, respectively). Complexes demonstrated different crystal packing of molecules. The electrochemical oxidation of the complexes involved the catecholate group as well as the thioether linker. The introduction of a thioether fragment into the aromatic ring of catechol ligand led to a shift in the potential of the “catechol/o-semiquinone” redox transition to the anodic region, which indicated the electron-withdrawing nature of the RS group. The radical scavenging activity of the complexes was determined in the reaction with DPPH radical

Lanthanide chloride complexes of amine-bis(phenolate) ligands and their reactivity in the ring-opening polymerization of ε-caprolactone

Reaction of two equivalents of n-BuLi with sterically demanding amine-bis(phenol) compounds, H2O2NN′R (Me2NCH2CH2N{CH2-3,5-R2-C6H2OH}2; R = t-Bu or t-Pe (tert-pentyl)) yields isolable lithium complexes, Li2(O2NN′R), in good yields. Upon reaction with one equivalent of LnCl3(THF)x, the lithium salts afford rare earth amine-phenolate chloride complexes in good yields, Ln(O2NN′R)Cl(THF); Ln = Y, Yb, Ho, Gd, Sm, Pr. Crystals of Y(O2NN′t-Bu)Cl(THF), 1, and Sm(O2NN′t-Bu)Cl(DME), 2, suitable for single crystal X-ray crystallographic analysis were obtained. In contrast to previously reported [{Gd(O2NN′t-Pe)(THF)(μ-Cl)}2] and related La and Sm complexes, these species are monomeric. 1 contains Y in a distorted octahedral environment bonded to two amine, two phenolate, one THF and one chloride donor. 2 contains Sm in a distorted capped trigonal prismatic environment bonded to two amine, two phenolate, two DME oxygens and one chloride donor. The Ln(O2NN′t-Pe)Cl(THF) complexes were active initators for the controlled ring-opening polymerization of ε-caprolactone with a tendency to form low molecular weight cyclic polyesters (Mn 3000–5000). The conversion rates, although slower than related amido and alkyl species, were different for monomeric and dimeric initiators. The size of the metal centre also affected the conversions and the molecular weights achieved

Binuclear Triphenylantimony(V) Catecholates through N-Donor Linkers: Structural Features and Redox Properties

A series of binuclear triphenylantimony(V) bis-catecholato complexes 1–11 of the type (Cat)Ph3Sb-linker-SbPh3(Cat) was prepared by a reaction of the corresponding mononuclear catecholates (Cat)SbPh3 with a neutral bidentate donor linker ligands pyrazine (Pyr), 4,4′-dipyridyl (Bipy), bis-(pyridine-4-yl)-disulfide (PySSPy), and diazobicyclo[2,2,2]octane (DABCO) in a dry toluene: Cat = 3,6-di-tert-butyl-catecholate (3,6-DBCat), linker = Pyr (1); PySSPy (2); Bipy (3); DABCO (4); Cat = 3,5-di-tert-butyl-catecholate (3,5-DBCat), linker = Bipy (5); DABCO (9); Cat = 4,5-(piperazine-1,4-diyl)-3,6-di-tert-butylcatecholate (pip-3,6-DBCat), linker = Bipy (6); DABCO (10); Cat = 4,5-dichloro-3,6-di-tert-butylcatecholate (4,5-Cl2-3,6-DBCat), linker = Bipy (7); DABCO (11); and Cat = 4,5-dimethoxy-3,6-di-tert-butylcatecholate (4,5-(MeO)2-3,6-DBCat), linker = Bipy (8). The same reaction of (4,5-Cl2-3,6-DBCat)SbPh3 with DABCO in an open atmosphere results in a formation of 1D coordination polymer {[(4,5-Cl2-3,6-DBCat)SbPh3·H2O]·DABCO}n (12). Bis-catecholate complex Ph3Sb(Cat-Spiro-Cat)SbPh3 reacts with Bipy as 1:1 yielding a rare macrocyclic tetranuclear compound {Ph3Sb(Cat-Spiro-Cat)SbPh3∙(Bipy)}2 (13). The molecular structures of 1, 3, 4, 5, 8, 10, 12, and 13 in crystal state were established by single-crystal X-ray analysis. Complexes demonstrate different types of relative spatial positions of mononuclear moieties. The nature of chemical bonds, charges distribution, and the energy of Sb...N interaction were investigated in the example of complex 5. The electrochemical behavior of the complexes depends on the coordinated N-donor ligand. The coordination of pyrazine, Bipy, and PySSPy at the antimony atom changes their mechanism of electrooxidation: instead of two successive redox stages Cat/SQ and SQ/Cat, one multielectron stage was observed. The coordination of the DABCO ligand is accompanied by a significant shift in the oxidation potentials of the catecholate ligand to the cathodic region (by 0.4 V), compared to the initial complex

Highly Active, Chemo- and Regioselective Yb II and Sm II Catalysts for the Hydrophosphination of Styrene with Phenylphosphine

International audienceStable heteroleptic amido YbII and SmII complexes bearing aminoether–phenolate ligands and devoid of coordinated solvent have been structurally characterized. They afford highly active, chemoselective and, in the case of monoadditions, 100% anti-Markovnikov regiospecific catalysts (down to 0.04 mol% loading) for the hydrophosphination of styrene with PhPH2 under mild conditions

Selective Intermolecular C–H Bond Activation: A Straightforward Synthetic Approach to Heteroalkyl Yttrium Complexes Containing a Bis(pyrazolyl)methyl Ligand

The reactions of bis­(pyrazolyl)­methanes CH₂(C₃HN₂R₂-3,5)₂ (R = Me, <i>t</i>Bu) with Y­(CH₂SiMe₃)₃(THF)₂ and LY­(CH₂SiMe₃)₂­(THF)_<i>n</i> (L = amidopyridinate (Ap′), amidinate (Amd), tridentate amidinate bearing 2-methoxyphenyl pendant in a side arm (Amd^OMe) and pentamethylcyclopentadienyl (Cp*); <i>n</i> = 0, 1) were investigated. CH₂(C₃HN₂<i>t</i>Bu₂-3,5)₂ turned out to be inert in these reactions, while less bulky CH₂(C₃HN₂Me₂-3,5)₂ easily undergoes metalation by yttrium alkyls. The reaction of Y­(CH₂SiMe₃)₃(THF)₂ with CH₂(C₃HN₂Me₂-3,5)₂ regardless of the molar ratio of the reagents affords a homoleptic tris­(alkyl) species, Y­[CH­(C₃HN₂Me₂-3,5)₂]₃ (<b>1</b>). However, the reactions of equimolar amounts of LY­(CH₂SiMe₃)₂(THF)_<i>n</i> and CH₂(C₃HN₂Me₂-3,5)₂ occur selectively with replacement of a sole CH₂SiMe₃ fragment and afford the related heteroalkyl complexes LY­(CH₂SiMe₃)­[CH­(C₃HN₂Me₂-3,5)₂]­(THF)_<i>n</i> (L = Ap′, <i>n</i> = 1 (<b>6</b>); Amd, <i>n</i> = 0 (<b>7</b>); Amd^OMe, <i>n</i> = 1 (<b>8</b>); Cp*, <i>n</i> = 1 (<b>9</b>)) in good yields. The second equivalent of CH₂(C₃HN₂Me₂-3,5)₂ does not react with heteroalkyl yttrium complexes. The X-ray studies revealed that in complexes <b>1</b> and <b>6</b>–<b>9</b> the bis­(pyrazolyl)­methyl ligands are bound to the yttrium centers in a similar fashion via one covalent Y–C and two coordination Y–N bonds. Thermal decomposition of complexes <b>6</b>–<b>9</b> (C₆D₆, 80 °C) as evidenced by ¹H NMR spectroscopy resulted in SiMe₄ elimination, while no activation of the C–H bonds of bis­(pyrazolyl)­methyl ligands was detected. When <b>6</b> was treated with an equimolar amount of PhSiH₃, only the YCH₂SiMe₃ bond selectively underwent σ-bond metathesis and a dimeric yttrium alkyl-hydrido complex, {Ap′Y­[CH­(C₃HN₂Me₂-3,5)₂]­(μ²-H)}₂ (<b>10</b>), was formed. The reaction of <b>6</b> with 2,6-diisopropylaniline also resulted in the selective protonation of the YCH₂SiMe₃ bond and cleanly afforded alkyl-anilido complex Ap′Y­(NHC₆H₃<i>i</i>Pr₂-2,6)­[CH­(C₃HN₂Me₂-3,5)₂]­(THF) (<b>11</b>). The ternary catalytic systems <b>6</b>–<b>9</b>/borate/Al<i>i</i>Bu₃ (borate = [HNMe₂Ph]­[B­(C₆F₅)₄], [Ph₃C]­[B­(C₆F₅)₄]; [Ln]:[borate]:[Al<i>i</i>Bu₃] = 1:1:10) demonstrated moderate catalytic activity in isoprene polymerization; they allow quantitative conversion into polymer of up to 1000 equiv of monomer in 2–4 h. The best activity and 1,4-cis selectivity (83.5%) were demonstrated by amidinato complex <b>8</b>

Polyfunctional Sterically Hindered Catechols with Additional Phenolic Group and Their Triphenylantimony(V) Catecholates: Synthesis, Structure, and Redox Properties

New polyfunctional sterically hindered 3,5-di-tert-butylcatechols with an additional phenolic group in the sixth position connected by a bridging sulfur atom&mdash;(6-(CH2-S-tBu2Phenol)-3,5-DBCat)H2 (L1), (6-(S-tBu2Phenol)-3,5-DBCat)H2 (L2), and (6-(S-Phenol)-3,5-DBCat)H2 (L3) (3,5-DBCat is dianion 3,5-di-tert-butylcatecolate)&mdash;were synthesized and characterized in detail. The exchange reaction between catechols L1 and L3 with triphenylantimony(V) dibromide in the presence of triethylamine leads to the corresponding triphenylantimony(V) catecholates (6-(CH2-S-tBu2Phenol)-3,5-DBCat)SbPh3 (1) and (6-(S-Phenol)-3,5-DBCat)SbPh3 (2). The electrochemical properties of catechols L1&ndash;L3 and catecholates 1 and 2 were investigated using cyclic voltammetry. The electrochemical oxidation of L1&ndash;L3 at the first stage proceeds with the formation of the corresponding o-benzoquinones. The second process is the oxidation of the phenolic moiety. Complexes 1 and 2 significantly expand their redox capabilities, owing to the fact that they can act as the electron donors due to the catecholate metallocycle capable of sequential oxidations, and as donors of the hydrogen atoms, thus forming a stable phenoxyl radical. The molecular structures of the free ligand L1 and complex 1 in the crystal state were determined by single-crystal X-ray analysis