Structural and dynamical aspects of alkylammonium salts of a silicodecatungstate as heterogeneous epoxidation catalysts

The structural and dynamical aspects of alkylammonium salts of a silicodecatungstate [(CH(3))(4)N](4)[γ-SiW(10)O(34)(H(2)O)(2)] [C1], [(n-C(3)H(7))(4)N](4)[γ-SiW(10)O(34)(H(2)O)(2)] [C3], [(n-C(4)H(9))(4)N](4)[γ-SiW(10)O(34)(H(2)O)(2)] [C4], and [(n-C(5)H(11))(4)N](4)[γ-SiW(10)O(34)(H(2)O)(2)] [C5] were investigated. The results of sorption isotherms, XRD analyses, and solid-state NMR spectroscopy show that facile sorption of solvent molecules, flexibility of structures, and high mobility of alkylammonium cations are crucial to the uniform distribution of reactant and oxidant molecules throughout the bulk solid, which are related to the high catalytic activities for epoxidation of alkenes.     

Dications of 3-phenylindenylidenefluorenes: evaluation of antiaromaticity of indenyl and fluorenyl cations by magnetic measures

Dications of p-substituted 3-phenylindenylidenefluorenes were prepared to examine the response of the resulting indenyl and fluorenyl cationic systems to magnetic measures of antiaromaticity. All measures, (1)H NMR shifts, nucleus independent chemical shifts (NICS(1)(zz)), and magnetic susceptibility exaltation, Lambda, supported the antiaromaticity of the dications 3a-f2+. The 1H NMR shifts and NICS(1)(zz) showed that the indenyl ring system was less antiaromatic than the fluorenyl ring system, contrary to the antiaromaticity of indenyl monocations compared to fluorenyl monocations. The presence of a phenyl substituent in the 3-position was able to stabilize the indenylidene cation through resonance, decreasing its antiaromaticity, but even in the absence of the 3-phenyl substituent, the indenyl system of indenylidenefluorene dications was less antiaromatic than the fluorenyl system. The decreased antiaromaticity of the 3-phenylindenylidenefluorene dications over the unsubstituted indenylidenefluorene dication was supported by (anti)aromatic (de)stabilization energy calculations, ASE.     

High-resolution characterization of liquid-crystalline [60]fullerenes using solid-state nuclear magnetic resonance spectroscopy

Liquid-crystalline materials containing fullerenes are valuable in the development of supramolecular switches and in solar cell technology. In this study, we characterize the liquid-crystalline and dynamic properties of fullerene-containing thermotropic compounds using solid-state natural abundance (13)C NMR experiments under stationary and magic angle spinning sample conditions. Chemical shifts spectra were measured in isotropic, liquid-crystalline nematic and smectic A and crystalline phases using one-dimensional (13)C experiments, while two-dimensional separated local-field experiments were used to measure the (1)H- (13)C dipolar couplings in mesophases. Chemical shift and dipolar coupling parameters were used to characterize the structure and dynamics of the liquid-crystalline dyads. NMR data of fullerene-containing thermotropic liquid crystals are compared to that of basic mesogenic unit and mesomorphic promoter compounds. Our NMR results suggest that the fullerene-ferrocene dyads form highly dynamic liquid-crystalline phases in which molecules rotate fast around the symmetry axis on the characteristic NMR time scale of approximately 10 (-4) s.     

C?NH2 Bond Formation Mediated by Iridium Complexes

In the presence of phosphanes (PR₃), the amido‐bridged trinuclear complex [{Ir(μ‐NH₂)(tfbb)}₃] (tfbb=tetrafluorobenzobarrelene) transforms into mononuclear discrete compounds [Ir(1,2‐η²‐4‐κ‐C₁₂H₈F₄N)(PR₃)₃], which are the products of the C N coupling between the amido moiety and a vinylic carbon of the diolefin. An alternative synthetic approach to these species involves the reaction of the 18 e⁻ complex [Ir(Cl)(tfbb)(PMePh₂)₂] with gaseous ammonia and additional phosphane. DFT studies show that both transformations occur through nucleophilic attack. In the first case the amido moiety attacks a diolefin coordinated to a neighboring molecule following a bimolecular mechanism induced by the highly basic NH₂ moiety; the second pathway involves a direct nucleophilic attack of ammonia to a coordinated tfbb molecule.     

CNH2 Bond Formation Mediated by Iridium Complexes

In the presence of phosphanes (PR₃), the amido‐bridged trinuclear complex [{Ir(μ‐NH₂)(tfbb)}₃] (tfbb=tetrafluorobenzobarrelene) transforms into mononuclear discrete compounds [Ir(1,2‐η²‐4‐κ‐C₁₂H₈F₄N)(PR₃)₃], which are the products of the C? N coupling between the amido moiety and a vinylic carbon of the diolefin. An alternative synthetic approach to these species involves the reaction of the 18 e^? complex [Ir(Cl)(tfbb)(PMePh₂)₂] with gaseous ammonia and additional phosphane. DFT studies show that both transformations occur through nucleophilic attack. In the first case the amido moiety attacks a diolefin coordinated to a neighboring molecule following a bimolecular mechanism induced by the highly basic NH₂ moiety; the second pathway involves a direct nucleophilic attack of ammonia to a coordinated tfbb molecule.     

Octahedral Ru(II) amido complexes TpRu(L)(L')(NHR) (Tp = hydridotris(pyrazolyl)borate; L = L' = P(OMe)3 or PMe3 or L = CO and L' = PPh3; R = H,Ph, or tBu): synthesis,characterization, and reactions with weakly acidic C-H bonds

The octahedral Ru(II) amine complexes [TpRu(L)(L')(NH(2)R)][OTf] (L = L' = PMe(3), P(OMe)(3) or L = CO and L' = PPh(3); R = H or (t)Bu) have been synthesized and characterized. Deprotonation of the amine complexes [TpRu(L)(L')(NH(3))][OTf] or [TpRu(PMe(3))(2)(NH(2)(t)Bu)][OTf] yields the Ru(II) amido complexes TpRu(L)(L')(NH(2)) and TpRu(PMe(3))(2)(NH(t)Bu). Reactions of the parent amido complexes or TpRu(PMe(3))(2)(NH(t)Bu) with phenylacetylene at room temperature result in immediate deprotonation to form ruthenium-amine/phenylacetylide ion pairs, and heating a benzene solution of the [TpRu(PMe(3))(2)(NH(2)(t)Bu)][PhC(2)] ion pair results in the formation of the Ru(II) phenylacetylide complex TpRu(PMe(3))(2)(C[triple bond]CPh) in >90% yield. The observation that [TpRu(PMe(3))(2)(NH(2)(t)Bu)][PhC(2)] converts to the Ru(II) acetylide with good yield while heating the ion pairs [TpRu(L)(L')(NH(3))][PhC(2)] yields multiple products is attributed to reluctant dissociation of ammonia compared with the (t)butylamine ligand (i.e., different rates for acetylide/amine exchange). These results are consistent with ligand exchange reactions of Ru(II) amine complexes [TpRu(PMe(3))(2)(NH(2)R)][OTf] (R = H or (t)Bu) with acetonitrile. The previously reported phenyl amido complexes TpRuL(2)(NHPh) [L = PMe(3) or P(OMe)(3)] react with 10 equiv of phenylacetylene at elevated temperature to produce Ru(II) acetylide complexes TpRuL(2)(C[triple bond]CPh) in quantitative yields. Kinetic studies indicate that the reaction of TpRu(PMe(3))(2)(NHPh) with phenylacetylene occurs via a pathway that involves TpRu(PMe(3))(2)(OTf) or [TpRu(PMe(3))(2)(NH(2)Ph)][OTf] as catalyst. Reactions of 1,4-cyclohexadiene with the Ru(II) amido complexes TpRu(L)(L')(NH(2)) (L = L' = PMe(3) or L = CO and L' = PPh(3)) or TpRu(PMe(3))(2)(NH(t)Bu) at elevated temperatures result in the formation of benzene and Ru hydride complexes. TpRu(PMe(3))(2)(H), [Tp(PMe(3))(2)Ru[double bond]C[double bond]C(H)Ph][OTf], [Tp(PMe(3))(2)Ru=C(CH(2)Ph)[N(H)Ph]][OTf], and [TpRu(PMe(3))(3)][OTf] have been independently prepared and characterized. Results from solid-state X-ray diffraction studies of the complexes [TpRu(CO)(PPh(3))(NH(3))][OTf], [TpRu(PMe(3))(2)(NH(3))][OTf], and TpRu(CO)(PPh(3))(C[triple bond]CPh) are reported.     

Backbone dynamics in the DNA HhaI protein binding site

The dynamics of the phosphodiester backbone in the [5'-GCGC-3'] 2 moiety of the DNA oligomer [d(G 1A 2T 3A 4 G 5 C 6 G 7 C 8T 9A 10T 11C 12)] 2 are studied using deuterium solid-state NMR (SSNMR). SSNMR spectra obtained from DNAs nonstereospecifically deuterated on the 5' methylene group of nucleotides within the [5'-GCGC-3'] 2 moiety indicated that all of these positions are structurally flexible. Previous work has shown that methylation reduces the amplitude of motion in the phosphodiester backbone and furanose ring of the same DNA, and our observations indicate that methylation perturbs backbone dynamics through not only a loss of mobility but also a change of direction of motion. These NMR data indicate that the [5'-GCGC-3'] 2 moiety is dynamic, with the largest amplitude motions occurring nearest the methylation site. The change of orientation of this moiety in DNA upon methylation may make the molecule less amenable to binding to the HhaI endonuclease.     

Influence of synthetic routes on the conformational order and mobility of C18 and C30 stationary phases

Silica gels modified with n-alkyl chains (n = 18, 30) are prepared by two different synthetic routes and are examined by variable temperature FTIR and solid-state NMR spectroscopy. HPLC measurements of SRM 869, cis/trans ss-carotene isomers and xanthophylls isomers confirm the dependence of the separation mechanism on the alkyl chain length and the synthetic routes. The determination of the silane functionality and degree of cross-linking of silane ligands on the silica surface is achieved by 29Si CP/MAS NMR measurements. The structural order and mobility of the alkyl chains are investigated by means of variable temperature 13C CP/MAS NMR measurements. Variable temperature FTIR studies are performed where conformational order and flexibility of the alkyl chains in C18 and C30 phases are monitored through conformational sensitive CH2 symmetric, anti-symmetric stretching and wagging modes. In addition, the chromatographic properties of the C18 and C30 phases are determined. The results derived from the FTIR, NMR and HPLC measurements are discussed in the context of the applied synthetic routes and alkyl chain lengths.     

H-bonding dependent structures of (NH4+)3H+(SO4 2-)2. Mechanisms of phase transitions

The role of different H-bonds in phases II, III, IV, and V of triammonium hydrogen disulfate, (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2), has been studied by X-ray diffraction and (1)H solid-state MAS NMR. The proper space group for phase II is C2/c, for phases III and IV is P2/n, and for phase V is P onemacr;. The structures of phases III and IV seem to be the same. The hydrogen atom participating in the O(-)-H(+).O(-) H-bond in phase II of (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2) at room temperature is split at two positions around the center of the crucial O(-)-H(+).O(-) H-bonding, joining two SO(4)(2)(-) tetrahedra. With decreasing temperature, it becomes localized at one of the oxygen atoms. Further cooling causes additional differentiation of possibly equivalent sulfate dimers. The NH(4)(+) ions participate mainly in bifurcated H-bonds with two oxygen atoms from sulfate anions. On cooling, the major contribution of the bifurcated H-bond becomes stronger, whereas the minor one becomes weaker. This is coupled with rotation of sulfate ions. In all the phases of (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2), some additional, weak but significant, reflections are observed. They are located between the layers of the reciprocal lattice, suggesting possible modulation of the host (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2) structure(s). According to (1)H MAS NMR obtained for phases II and III, the nature of the acidic proton disorder is dynamic, and localization of the proton takes place in a broader range of temperatures, as can be expected from the X-ray diffraction data.     

"Alkaline-earth metals in a box": structures of solvent-separated ion pairs

During our research on homoleptic organocalcium compounds, we found that fluorenylcalcium complexes show unusual solution behavior and precipitate from nonpolar solvents after addition of THF. Their solid-state structures reveal the unexpected rupture of both metal-carbanion bonds by the polar solvent THF. The crystal structures of five new Mg and Ca solvent-separated ion pairs are described. The compound [Ca(2+)(thf)(6)][Me(3)Si(fluorenyl(-))](2) is the first organometallic complex of a Group 2 element that crystallizes as a completely solvent-separated ion pair. The driving forces for its formation are: 1) the strong Ca-THF bond; 2) the stability of the free [Me(3)Si(fluorenyl)](-) ion; 3) encapsulation of [Ca(2+)(thf)(6)] in a "box", the walls of which consist of anionic fluorenyl ligands and benzene molecules; and 4) the presence of numerous (THF)C- H...pi interactions. The magnesium analogue [Mg(2+)(thf)(6)][Me(3)Si(fluorenyl(-))](2) is isostructural. Bis(7,9-diphenylcyclopenta[a]acenaphthadienyl)calcium also crystallizes as a completely solvent-separated ion pair and can likewise be described as a [Ca(2+)(thf)(6)] species in a box of delocalized anions and benzene molecules. In addition, the structures of two Ph(4)B(-) complexes of Mg and Ca are described. [Mg(2+)(thf)(6)][Ph(4)B(-)](2) crystallizes as a completely solvent-separated ion pair and also shows a solvated metal cation bonded via C-H.pi interactions in a cavity formed by Ph(4)B(-) ions. [(thf)(4)CaBr(+)][Ph(4)B(-)] has a structure in which one of the anionic ligands is still bonded to the Ca atom. Bridging bromide ligands result in the formation of the dimer [(thf)(4)CaBr(+)](2).     

Lyotropic and thermotropic phase transitions in films of ionene-alkyl sulfate complexes

Five [X,Y]-ionenes [(CH2)(X)N+(CH3)2(CH2)(Y)N+(CH3)2]nBr-(2n) were prepared (X = 3, 5; Y = 10, 12, 22). Using new preparation methods, dry, salt-free complexes with three n-alkyl sulfates (octyl, decyl, and dodecyl) were obtained. The ionenes and their complexes were characterized in methanol solution by light scattering, viscometry, and fluorescent probe studies. The solid materials were investigated by means of DSC, TG, and ATR-IR. Transparent films were formed from stoichiometric [3,10], [3,12], and [5,10]-ionene complexes with decyl and dodecyl sulfate. In the films, mesogenic phase transitions could be induced: dry films were optically isotropic; when exposed to elevated humidity, the films slowly became optically anisotropic because of a lyotropic transition to a hexagonal mesogenic phase. The relative humidity, at which the hexagonal phase developed, was distinct for each complex. The anisotropic phases were converted to isotropic in a thermotropic transition under controlled relative humidity at specific clearing temperatures, which were higher for dodecyl complexes than for decyl complexes. This thermotropic isotropic-anisotropic transition could be cycled several times, but partial hydrolysis of the alkyl sulfates reduced the reproducibility of transition points.     

Ruthenium nanoparticles inside porous [Zn4O(bdc)3] by hydrogenolysis of adsorbed [Ru(cod)(cot)]: a solid-state reference system for surfactant-stabilized ruthenium colloids

The gas-phase loading of [Zn4O(bdc)3] (MOF-5; bdc = 1,4-benzenedicarboxylate) with the volatile compound [Ru(cod)(cot)] (cod = 1,5-cyclooctadiene, cot = 1,3,5-cyclooctatriene) was followed by solid-state (13)C magic angle spinning (MAS) NMR spectroscopy. Subsequent hydrogenolysis of the adsorbed complex inside the porous structure of MOF-5 at 3 bar and 150 degrees C was performed, yielding ruthenium nanoparticles in a typical size range of 1.5-1.7 nm, embedded in the intact MOF-5 matrix, as confirmed by transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (PXRD), and X-ray absorption spectroscopy (XAS). The adsorption of CO molecules on the obtained Ru@MOF-5 nanocomposite was followed by IR spectroscopy. Solid-state (2)H NMR measurements indicated that MOF-5 was a stabilizing support with only weak interactions with the embedded particles, as deduced from the surprisingly high mobility of the surface Ru-D species in comparison to surfactant-stabilized colloidal Ru nanoparticles of similar sizes. Surprisingly, hydrogenolysis of the [Ru(cod)(cot)]3.5@MOF-5 inclusion compound at the milder condition of 25 degrees C does not lead to the quantitative formation of Ru nanoparticles. Instead, formation of a ruthenium-cyclooctadiene complex with the arene moiety of the bdc linkers of the framework takes place, as revealed by (13)C MAS NMR, PXRD, and TEM.     

Conformational analysis of 1,3-benzenediol dibenzoate as a model of banana-shaped molecules forming chiral smectic phases

Banana-shaped molecules, e.g. 1,3-phenylene bis[4-(4-n-alkoxyphenyliminomethyl)benzoates] and 1,3-phenylene bis[4-(4-n-alkylphenyliminomethyl)benzoates], form ferroelectric and chiral smectic phases without a chiral carbon. ¹³C NMR measurement suggested that 1,3-benzenediol dibenzoate (BD) moiety assumes asymmetrically twisted conformation which may be ascribed to the chirality of the phases. In this study, conformational analysis was carried out for BD by using the density functional theory (DFT) calculation. The results indicated that the asymmetrical twist conformation of the BD moiety is most stable.     

Synthesis and reactivity of the monomeric late-transition-metal parent amido complex [Ir(Cp*)(PMe3)(Ph)(NH2)

The late-transition-metal parent amido compound [Ir(Cp*)(PMe3)(Ph)(NH2)] (2) has been synthesized by deprotonation of the corresponding ammine complex [Ir(Cp*)(PMe3)(Ph)(NH3)][OTf] (6) with KN(SiMe3)2. An X-ray structure determination has ascertained its monomeric nature. Proton-transfer studies indicate that 2 can successfully deprotonate p-nitrophenylacetonitrile, aniline, and phenol. Crystallographic analysis has revealed that the ion pair [Ir(Cp*)(PMe3)(Ph)(NH3)][OPh] (8) exists as a hydrogen-bonded dimer in the solid state. Reactions of 2 with isocyanates and carbodiimides lead to overall insertion of the heterocumulenes into the N--H bond of the Ir-bonded amido group, demonstrating the ability of 2 to act as an efficient nucleophile. Intriguing reactivity is observed when amide 2 reacts with CO or 2,6-dimethylphenyl isocyanide. eta4-Tetramethylfulvene complexes [Ir(eta4-C5Me4CH2)(PMe3)(Ph)(L)] (L=CO (15), CNC6H3-2,6-(CH3)2 (16)) are formed in solution through displacement of the amido group by the incoming ligand followed by deprotonation of a methyl group on the Cp* ring and liberation of ammonia. Conclusive evidence for the presence of the Ir-bonded eta4-tetramethylfulvene moiety in the solid state has been provided by an X-ray diffraction study of complex 16.     

Aluminum complexes incorporating bidentate amido phosphine ligands

A series of aluminum complexes supported by o-phenylene-derived amido phosphine ligands, N-(2-diphenylphosphinophenyl)-2,6-dimethylanilide ([Me-NP]-) and N-(2-diphenylphosphinophenyl)-2,6-diisopropylanilide ([iPr-NP]-), have been prepared. The reactions of trialkylaluminum with H[Me-NP] and H[iPr-NP], respectively, in refluxing toluene produced the corresponding dialkyl complexes [Me-NP]AlR(2) and [iPr-NP]AlR(2) (R = Me, Et). Deprotonation of H[Me-NP] with n-BuLi in THF at -35 degrees C followed by addition of AlCl(3) in toluene at -35 degrees C afforded [Me-NP]AlCl(2), which was subsequently reacted with 2 equiv of trimethylsilylmethyllithium in toluene to give [Me-NP]Al(CH(2)SiMe(3))(2). The aluminum complexes were all characterized by (1)H, (13)C, (31)P, and (27)Al NMR spectroscopy. The solid-state structures of monomeric, four-coordinate [Me-NP]AlEt(2) and [iPr-NP]AlMe(2) and five-coordinate [Me-NP]AlCl(2)(THF) were determined by X-ray crystallography. The (1)H NMR studies of [Me-NP]AlEt(2), [Me-NP]Al(CH(2)SiMe(3))(2), and [iPr-NP]AlEt(2) indicate diastereotopic alpha-hydrogen atoms in these molecules. Heteronuclear COSY and NOE experiments suggest that the phosphorus donor in [Me-NP]Al(CH(2)SiMe(3))(2) and [iPr-NP]AlEt(2) is coupled to only one of the diastereotopic alpha-hydrogen atoms that is virtually antiperiplanar with respect to the phosphorus atom.     

UV-Vis, NMR, and time-resolved spectroscopy analysis of photoisomerization behavior of three- and six-azobenzene-bound tris(bipyridine)cobalt complexes

The photoisomerization properties of tris(bipyridine)cobalt complexes containing six or three azobenzene moieties, namely, [Co(II)(dmAB)3](BF4)2 [dmAB = 4,4'-bis[3'-(4'-tolylazo)phenyl]-2,2'-bipyridine], [Co(III)(dmAB)3](BF4)3, [Co(II)(mAB)3](BF4)2 [mAB = 4-[3' '-(4' '-tolylazo)phenyl]-2,2'-bipyridine], and [Co(III)(dmAB)3](BF4)3, derived from the effect of gathering azobenzenes in one molecule and the effect of the cobalt(II) or cobalt(III) ion were investigated using UV-vis absorption spectroscopy, femtosecond transient spectroscopy, and 1H NMR spectroscopy. In the photostationary state of these four complexes, nearly 50% of the trans-azobenzene moieties of the Co(II) complexes were converted to the cis isomer, and nearly 10% of the trans-azobenzene moieties of the Co(III) complexes isomerized to the cis isomer, implying that the cis isomer ratio in the photostationary state upon irradiation at 365 nm is controlled not by the number of azobenzene moieties in one molecule but rather by the oxidation state of the cobalt ions. The femtosecond transient absorption spectra of the ligands and the complexes suggested that the photoexcited states of the azobenzene moieties in the Co(III) complexes were strongly deactivated by electron transfer from the azobenzene moiety to the cobalt center to form an azobenzene radical cation and a Co(II) center. The cooperation among the photochemical structural changes of six azobenzene moieties in [Co(II)(dmAB)3](BF4)2 was investigated with 1H NMR spectroscopy. The time-course change in the 1H NMR signals of the methyl protons indicated that each azobenzene moiety in [Co(II)(dmAB)3](BF4)2 isomerized to a cis isomer with a random probability of 50% and without interactions among the azobenzene moieties.     

Synthesis, characterization of bridged bis(amidinate) lanthanide amides and their application as catalysts for addition of amines to nitriles for monosubstituted N-arylamidines

A series of lanthanide amide complexes supported by bridged bis(amidinate) ligand L, LLnNHAr(1)(DME) (L = [Me(3)SiNC(Ph)N(CH(2))(3)NC(Ph)NSiMe(3)], Ar(1) = 2,6-(i)Pr(2)C(6)H(3), DME = dimethoxyethane, Ln = Y (1), Pr (2), Nd (3), Gd (4), Yb (5)), [Yb(μ(2)-NHPh)](2)(μ(2)-L)(2) (6) and [LYb](2)(μ(2)-NHAr(2))(2) (7) (Ar(2) = (o-OMe)C(6)H(4)), were synthesized by reaction of LLnCl(THF)(2) with the corresponding lithium amide in good yields and structurally characterized by X-ray crystal structure analyses. All complexes were found to be precatalysts for the catalytic addition of aromatic amines to aromatic nitriles to give monosubstituted N-arylamidines. The catalytic activity was influenced by lanthanide metals and the amido groups with the active sequence of Y (1) < Gd (4) < Nd (3) < Pr (2) ～ Yb (5) for the lanthanide metals and -NHAr(2) < -NHPh < -NHAr(1) for the amido groups. The catalytic addition reaction with complex 5 showed a good scope of aromatic amines. Some key reaction intermediates were isolated and structurally characterized, including the amidinate complexes LLn[NPhCNAr(1)](PhCN) (Ln = Y (8), Ln = Yb (9)), LYb[NAr(2)CNAr(1)](Ar(2)CN) (10), and amide complex 5 prepared by protonation of 9 by Ar(1)NH(2). Reactivity studies of these complexes suggest that the present catalytic formation of monosubstituted N-arylamidines proceeds through nucleophilic addition of an amido species to a nitrile, followed by amine protonolysis of the resultant amidinate species.     

New reactivity and structural insights of alkali-metal-mediated alumination in directed ortho-alumination of a tertiary aromatic amide

The first reported sodium alkyl(TMP)aluminate reagent to be synthesised and crystallographically characterised, [TMEDA.Na(mu-TMP)(mu-(I)Bu)Al((I)Bu)2], reacts as an amido base towards phenylacetylene to form crystalline [(TMEDA)2.Na(mu-CCPh)(mu-(I)Bu)Al((I)Bu)2]; whereas the congeneric TMEDA-stabilised lithium (TMP)aluminate exhibits dual alkyl/amido basicity in its reaction with N,N-diisopropylbenzamide to form a novel heterobimetallic-heterotrianionic crystalline complex [{PhC(=O)N(iPr)2}.Li{2-[1-C(=O)N(iPr)2]C6H4}{Me2NCH2CH2N(Me)CH2}Al(iBu)2], which, in addition to having an ortho-deprotonated benzamide ligand, also contains a methyl-deprotonated TMEDA ligand and a neutral benzamide molecule ligated to lithium.     

Copolymerization of ethylene with 1,1‐disubstituted olefins catalyzed by ansa‐(fluorenyl)(cyclododecylamido)dimethyltitanium complexes

A series of titanium complexes with ansa‐(fluorenyl)(cyclododecylamido) ligands, Me₂Si(η³‐R)(N‐c‐C₁₂H₂₃)TiMe₂ [R = fluorenyl ( 5 ), 2,7‐^tBu₂fluorenyl ( 6 ), 3,6‐^tBu₂fluorenyl ( 7 )], was synthesized. The crystal structure of complex 6 revealed η³‐coordination of the fluorenyl moiety to the metal. Upon activation with trialkylaluminum‐free modified methylaluminoxane, complexes 5 – 7 as well as the corresponding ^tBu amide complexes, Me₂Si(η³‐R)(N^tBu)TiMe₂ [R = fluorenyl ( 2 ), 2,7‐^tBu₂fluorenyl ( 3 ), 3,6‐^tBu₂fluorenyl ( 4 )], were adopted as the catalysts for the copolymerization of ethylene (E) and isobutylene (IB). Among these complexes, complex 6 was found to achieve the highest IB incorporation to produce alternating E‐IB copolymers. Complex 6 system also achieved copolymerization of E and limonene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Interaction between f-electronic systems in dinuclear lanthanide complexes with phthalocyanines

The first detection and characterization of the interactions between the f-electronic systems in the dinuclear complexes of paramagnetic trivalent Tb, Dy, Ho, Er, Tm, and Yb ions with phthalocyanine ligands are presented. The molar magnetic susceptibilities, chi(m), were measured for PcLnPcLnPc* ([Ln, Ln]; Pc = dianion of phthalocyanine, Pc* = dianion of 2,3,9,10,16,17,23,24-octabutoxyphthalocyanine) and PcLnPcYPc* ([Ln, Y]) in the range from 1.8 K to room temperature. The selective synthetic method previously reported for the heterodinuclear complex [Y, Ln] was used to prepare [Ln, Ln] and [Ln, Y] with a modification on the choice of starting materials. The f-f interaction contributions to the magnetic susceptibility are evaluated as Delta(chi)(m)T = chi(m)([Ln, Ln])T - chi(m)([Ln, Y])T - chi(m)([Y, Ln])T, where T refers to temperature on the kelvin scale. The homodinuclear complexes having f(8)-f(10)-systems, namely [Tb, Tb], [Dy, Dy], and [Ho, Ho], show positive Delta(chi)(m)T values in the 1.8-50 K range, indicating the existence of ferromagnetic interaction between the f-systems. The magnitude of the Delta(chi)(m)T increases in the descending order of the number of f-electrons. [Er, Er] gives negative Delta(chi)(m)T values in the 1.8-50 K range, showing the antiferromagnetic nature of the f-f interaction. [Tm, Tm] exhibits small and negative Delta(chi)(m)T values, which gradually decline in the negative direction as the temperature decreases in the range 13-50 K and sharply rise in the positive direction as the temperature falls from 10 to 1.8 K. [Yb, Yb] has extremely small Delta(chi)(m)T values, whose magnitude at 2 K is less than 1% of that of [Tb, Tb]. The ligand field parameters of the ground-state multiplets of the six [Ln, Y] complexes are determined by simultaneous fitting to both the magnetic susceptibility data and paramagnetic shifts of (1)H NMR. The theoretical analysis successfully converged by assuming that each ligand field parameter is a function of the number of f-electrons in each ion. Using these parameters as well as the previously obtained corresponding parameters for the [Y, Ln] series, the interactions between the f-systems in [Ln, Ln] are investigated. All the characteristic observations above are satisfactorily reproduced with the assumption that the magnetic dipolar term is the sole source of the f-f interaction.