Titanium complexes with sulfur‐linked bis(phenolate) ligands

High‐quality crystals of two bis(phenolate)titanium complexes, namely dichlorido{4,4′‐dimethyl‐2,2′‐[cyclohexane‐1,2‐diylbis(sulfanediyl)]diphenolato}titanium(IV), [Ti(C₂₀H₂₂O₂S₂)Cl₂], (I), and dichlorido{2,2′‐[cyclohexane‐1,2‐diylbis(sulfanediyl)]diphenolato}titanium(IV), [Ti(C₁₈H₁₈O₂S₂)Cl₂], (II), were obtained by reactive crystallization. Depending on the solvent, compound (II) was obtained as unsolvated (IIa) or as the toluene hemisolvate, [Ti(C₁₈H₁₈O₂S₂)Cl₂]·0.5C₇H₈, (IIb). These systems without bulky substituents on the aromatic phenolate rings serve as ideal model compounds for precatalysts. The excellent X‐ray diffraction data will help clarify the nature of the mismatched interactions between the soft S atoms within the ligand and the hard titanium center. Molecule (I) has crystallographic C₂ symmetry.     

Synthetic and structural investigations of alkali metal diamine bis(phenolate) complexes

Two lithium and one sodium diamine bis(phenolate) complexes have been prepared and characterised by X-ray crystallography and NMR spectroscopy. Two parent diamine bis(phenol) ligands were utilised in the study (1-H2 and 2-H2). Dimeric (1-Li2)(2) was prepared by treating 1-H2 with two molar equivalents of n-butyllithium in hydrocarbon solvent. It adopts a ladder-like structure in the solid state, which appears to deaggregate in C6D6 solution. The monomeric (hence, dinuclear) TMEDA-solvated species [2-Li(2).(TMEDA)] has two chemically unique Li atoms in the solid state and is prepared by reacting 2-H2 with two molar equivalents of n-butyllithium in hydrocarbon solvent, in the presence of N,N,N',N'-tetramethylethylenediamine (TMEDA). Finally, the dimeric sodium-based [2-Na(2) x (OEt2](2) was prepared by reacting 1-H2 with two molar equivalents of freshly prepared n-butylsodium in a hydrocarbon-diethyl ether medium. The complex adopts a Na4O4) cuboidal structure in the solid state, which appears to remain intact in C6D6 solution.     

Diamine bis(phenolate) and pendant amine bis(phenolate) ligands: catalytic activity for the room temperature palladium‐catalyzed Suzuki–Miyaura coupling reaction

A series of amine bis(phenolate) ligands bearing aryl substituents of varying steric bulk are reported and characterized using single‐crystal X‐ray diffraction, NMR spectroscopy and high‐resolution mass spectrometry experiments. Palladium complexes derived in situ from these ligands are evaluated as catalysts for the Suzuki–Miyaura coupling of phenylboronic acid and aryl bromides. High conversions are observed for these reactions in methanol solvent at low catalyst loadings (0.01 mol%), short reaction times (30 min) and mild temperatures (30°C). Conversion is observed for a range of substrates, and is found to depend on the nature of the external base and solvent employed. These findings demonstrate the utility of catalysts derived from late transition metal complexes of amine bis(phenolate) ligands, particularly those bearing bulky cumyl substituents. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and molecular structure of piperazidine-bridged bis(phenolate) samarium(II) complex and its reactivity to carbodiimides

The reaction of Sm[N(TMS)(2)](2)(THF)(2) with H(2)L (L = 1,4-bis(2-hydroxy-3-tert-butyl-5-methyl-benzyl)-piperazidine) afforded [SmL(HMPA)(2)](4)·8THF 2 upon treatment with 2 equivalents of HMPA (hexamethyl phosphoric triamide). X-ray crystallographic analysis of 2 reveals a tetrametallic macrocyclic structure, which represents the first example of a crystal structure of a Sm(II) complex stabilized by heteroatom bridged bis(phenolate) ligands. Reduction of carbodiimides RNCNR (R = (i)Pr and Cy) by [SmL](2)(THF) 1, which was formed in situ by the reaction of Sm[N(TMS)(2)](2)(THF)(2) with H(2)L in THF, yielded the Sm(III) complex with an oxalamidinate ligand [LSm{(N(i)Pr)(2)CC(N(i)Pr)(2)}SmL]·THF 3 for (i)PrNCN(i)Pr and the Sm(III) complex with a diamidocarbene ligand [LSm(μ-CyNCNCy)SmL]·5.5THF 4 for CyNCNCy.     

Synthesis,structure, and properties of the Sc chloride complex coordinated by the tridentate bis(phenolate)-tethered NHC ligand

The scandium chloride complex LScCl(py)₂ (L is bis[(2,4-di-tert-butyl)phenolato]-6,6′-(4,5-dihydroimidazol-2-ylidene)) containing the dianionic bis(phenolate)-tethered N-heterocyclic carbene (NHC) ligand was synthesized. The X-ray diffraction study demonstrated that the complex has a mononuclear structure with intramolecular coordination of the carbene moiety to the Sc³⁺ ion. In the presence of moist air, the NHC moiety is hydrolyzed, resulting in the formation of the chloride complex [L’ScCl(py)]₂ with the dianionic tetradentate bis(phenolate) ligand containing the [NH(CH)₂N(HC=O)] linker. The binuclear complex [L’ScClpy]₂ is formed through the coordination of the oxygen atom of the formylethylenediamine moiety to the second Sc³⁺ ion.

     

The reactions of some organotin(IV) chlorides with antimony(V) chloride and boron(III) chloride

The reactions of the organotin chlorides R_nSnCl_4?n(R = Me or Ph; ? n ? 4) with the Lewis acids SbCl₅ and BCl₃ have been investigated by ¹¹⁹Sn and (where appropriate) ¹¹B NMR spectroscopy. The results show that transfer of organo-groups to antimony or boron usually takes place rather than chloride abstraction to give cationic tin(IV) species, and this process is more facile for phenyl than methyl groups. These conclusions have been confirmed in some instances by isolation of the non-volatile reaction products.     

Aerobic oxidation reactions catalyzed by vanadium complexes of bis(phenolate) ligands

Vanadium(V) complexes of the tridentate bis(phenolate)pyridine ligand H(2)BPP (H(2)BPP = 2,6-(HOC(6)H(2)-2,4-(t)Bu(2))(2)NC(5)H(3)) and the bis(phenolate)amine ligand H(2)BPA (H(2)BPA = N,N-bis(2-hydroxy-4,5-dimethylbenzyl)propylamine) have been synthesized and characterized. The ability of the complexes to mediate the oxidative C-C bond cleavage of pinacol was tested. Reaction of the complex (BPP)V(V)(O)(O(i)Pr) (4) with pinacol afforded the monomeric vanadium(IV) product (BPP)V(IV)(O)(HO(i)Pr) (6) and acetone. Vanadium(IV) complex 6 was oxidized rapidly by air at room temperature in the presence of NEt(3), yielding the vanadium(V) cis-dioxo complex [(BPP)V(V)(O)(2)]HNEt(3). Complex (BPA)V(V)(O)(O(i)Pr) (5) reacted with pinacol at room temperature, to afford acetone and the vanadium(IV) dimer [(BPA)V(IV)(O)(HO(i)Pr)](2). Complexes 4 and 5 were evaluated as catalysts for the aerobic oxidation of 4-methoxybenzyl alcohol and arylglycerol β-aryl ether lignin model compounds. Although both 4 and 5 catalyzed the aerobic oxidation of 4-methoxybenzyl alcohol, complex 4 was found to be a more active and robust catalyst for oxidation of the lignin model compounds. The catalytic activities and selectivities of the bis(phenolate) complexes are compared to previously reported catalysts.     

Conformational studies of dicyclohexylthallium chloride,bis(4-methylcyclohexyl)thallium chloride and bis(4-tert-butylcyclohexyl)thallium chloride by 1H NMR

Vicinal thallium–hydrogen coupling constants are used to discuss conformations in dicyclohexylthallium chloride, bis(4-methylcyclohexyl)thallium chloride and bis(4-tert-butylcyclohexyl)thallium chloride. Thallium does not have a very strong preference for equatorial positions in dicyclohexylthallium chloride, whereas bis(4-alkylcyclohexyl)thallium chlorides exist largely in one conformation. Bis(4-methylcyclohexyl)thallium chloride exists in three isomeric forms; the major product appears to be the cis-isomer (equatorial methyl, axial thallium), with the other two isomers probably containing thallium trans to the methyl group (axial thallium being preferred). The preference for the cis-isomer (equatorial tert-butyl, axial thallium) of bis(4-tert-butylcyclohexyl)thallium chloride is such that other isomers are not obtained.     

Synthesis, characterization and reactivity of heteroleptic rare earth metal bis(phenolate) complexes

The synthesis, characterization and reactivity of heteroleptic rare earth metal complexes supported by the carbon-bridged bis(phenolate) ligand 2,2'-methylene-bis(6-tert-butyl-4-methyl-phenoxo) (MBMP(2-)) are described. Reaction of (C(5)H(5))(3)Ln(THF) with MBMPH(2) in a 1 : 1.5 molar ratio in THF at 50 degrees C produced the heteroleptic rare earth metal bis(phenolate) complexes (C(5)H(5))Ln(MBMP)(THF)(n) (Ln = La, n = 3 (); Ln = Yb (), Y (), n = 2) in nearly quantitative yields. The residual C(5)H(5)(-) groups in complexes to can be substituted by the bridged bis(phenolate) ligands at elevated temperature to give the neutral rare earth metal bis(phenolate) complexes, and the ionic radii have a profound effect on the structures of the final products. Complex reacted with MBMPH(2) in a 1 : 0.5 molar ratio in toluene at 80 degrees C to produce a dinuclear complex (MBMP)La(THF)(mu-MBMP)(2)La(THF)(2) () in good isolated yield; whereas complexes and reacted with MBMPH(2) under the same conditions to give (MBMP)Ln(MBMPH)(THF)(2) (Ln = Yb (), Y ()) as the final products, in which one hydroxyl group of the phenol is coordinated to the rare earth metal in a neutral fashion. The reactivity of complexes and with some metal alkyls was explored. Reaction of complex with 1 equiv. of AlEt(3) in toluene at room temperature afforded unexpected ligand redistributed products, and a discrete ion pair ytterbium complex [(MBMP)Yb(THF)(2)(DME)][(MBMP)(2)Yb(THF)(2)] () was isolated in moderate yield. Furthermore, reaction of complex with 1 equiv. of ZnEt(2) in toluene gave a ligand redistributed complex [(mu-MBMP)Zn(THF)](2) () in reasonable isolated yield. Similar reaction of complex with ZnEt(2) also afforded complex ; whereas the reaction of complex with 1 equiv. of n-BuLi in THF afforded the heterodimetallic complex [(THF)Yb(MBMP)(2)Li(THF)(2)] (). All of these complexes were well characterized by elemental analyses, IR spectra, and single-crystal structure determination, in the cases of complexes , and -.     

Structural diversity of indium complexes containing a tetradentate (OSSO)-type bis(phenolate) ligand

Indium bis(phenolato) complexes [{In(CH₃)₂(THF)}₂(L)] (L = 1,4-dithiabutanediylbis(4,6-di-tert-butylphenolato) (etbbp), 2) and [In(cytp)(CH₃)]₂ (L = (1,2-cyclohexanediyldithio)-2,2′-diphenolato (rac-cytp), 3) were prepared from [In(CH₃)₃] and the tetradentate 1,2-dithiaalkanediyl-bridged bis(phenol) LH₂. The nature of the ligand bridging two indium centers was shown by X-ray diffraction studies of the complex [{In(CH₃)₂(THF)}₂(etbbp)] (2) that was synthesized from complex [In(etbbp)(CH₃)(THF)_n] (1) by reaction with a second equivalent of [In(CH₃)₃]. A related ligand without bulky substituents on the aromatic rings leads to the dimeric compound [In(cytp)(CH₃)]₂ (3) with distorted octahedral configuration in the solid state. It was converted into the cation [In(cytp)]⁺ by methyl abstraction with [B(C₆F₅)₃].     

Synthesis of volatile bis[bis(trimethylsilyl)amide]-substituted boron derivatives

Russian Journal of General Chemistry - General strategy for the synthesis of organoboron compounds containing bis(trimethylsilyl)amide substituents has been suggested.     

Novel iron(III) complexes of tripodal and linear tetradentate bis(phenolate) ligands: close relevance to intradiol-cleaving catechol dioxygenases

Four new iron(III) complexes of the bis(phenolate) ligands N,N-dimethyl-N',N'-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine [H2(L1)], N,N-dimethyl-N',N'-bis(2-hydroxy-4-nitrobenzyl)ethylenediamine [H2(L2)], N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine [H2(L3)], and N,N'-dimethyl-N,N'-bis(2-hydroxy-4-nitrobenzyl)ethylenediamine [H2(L4)] have been isolated and studied as structural and functional models for the intradiol-cleaving catechol 1,2-dioxygenases (CTD). The complexes [Fe(L1)Cl] (1), [Fe(L2)(H2O)Cl] (2), [Fe(L3)Cl] (3), and [Fe(L4)(H2O)Cl] (4) have been characterized using absorption spectral and electrochemical techniques. The single-crystal X-ray structures of the ligand H2(L1) and the complexes 1 and 2 have been successfully determined. The tripodal ligand H2(L1) containing a N2O2 donor set represents the metal-binding region of the iron proteins. Complex 1 contains an FeN2O2Cl chromophore with a novel trigonal bipyramidal coordination geometry. While two phenolate oxygens and an amine nitrogen constitute the trigonal plane, the other amine nitrogen and chloride ion are located in the axial positions. In contrast, 2 exhibits a rhombically distorted octahedral coordination geometry for the FeN2O3Cl chromophore. Two phenolate oxygen atoms, an amine nitrogen atom, and a water molecule are located on the corners of a square plane with the axial positions being occupied by the other nitrogen atom and chloride ion. The interaction of the complexes with a few monodentate bases and phenolates and differently substituted catechols have been investigated using absorption spectral and electrochemical methods. The effect of substituents on the phenolate rings on the electronic spectral features and FeIII/FeII redox potentials of the complexes are discussed. The interaction of the complexes with catecholate anions reveals changes in the phenolate to iron(III) charge-transfer band and also the appearance of a low-energy catecholate to iron(III) charge-transfer band similar to catechol dioxygenase-substrate complexes. The redox behavior of the 1:1 adducts of the complexes with 3,5-di-tert-butylcatechol (H2DBC) has been also studied. The reactivities of the present complexes with H2DBC have been studied and illustrated. Interestingly, only 2 and 4 catalyze the intradiol-cleavage of H2DBC, the rate of oxygenation being much faster for 4. Also 2, but not 4, yields an extradiol cleavage product. The reactivity of the complexes could be illustrated not on the basis of the Lewis acidity of the complexes alone but by assuming that the product release is the rate-determining phase of the catalytic reaction.     

Synthesis, characterization and reactivity of a zwitterionic amine bridged bis(phenolate) lanthanide complex

A zwitterionic amine bridged bis(phenolate) ytterbium(III) complex was synthesized, and its reactivity with a zinc cluster was explored. The reaction of (C₅H₅)₃Yb(THF) with the amine bridged bis(phenol) HONNOH [ONNO = Me₂NCH₂CH₂N{CH₂-(2-O-C₆H₂-Bu^t₂-3,5)}₂] in a 1:2 M ratio in toluene at 80 °C produced the zwitterionic ytterbium complex [ONNO]Yb[ONNO(μ₄-H)] (1) in a high isolated yield. The reaction of ZnEt₂ with 1 equiv of PhCH₂OH gave a zinc cluster Zn₇Et₆(OCH₂Ph)₈ (2) in a good isolated yield. Complex 1 reacted with complex 2 in a 7:1 M ratio at room temperature to afford the unexpected ligand redistributed product [ONNO]Zn(THF) (3). These complexes were well characterized by elemental analyses, IR spectra and NMR spectroscopy in the case of complexes 2 and 3. The definitive molecular structures of complexes 2 and 3 were determined by single-crystal X-ray analyses.     

Living polymerization and block copolymerization of alpha-olefins by an amine bis(phenolate) titanium catalyst

An amine bis(phenolate) dibenzyl titanium complex having a methoxy donor on a side arm leads, upon activation with tris(pentafluorophenyl)borane, to unique living properties in alpha-olefin polymerization: exceptionally high molecular weight poly(1-hexene) is obtained in a living fashion at room temperature, living polymerization of 1-hexene is obtained above room temperature, and block copolymerization of 1-hexene and 1-octene at room temperature is described as well.