Coinage metal complexes of a boron-substituted soft scorpionate ligand

An improved synthesis of lithium phenyltris(methimazolyl)borate, Li[PhTm(Me)], (methimazole = 1-methylimidazole-2-thione) is described, and the structure of the methanol-solvated [Li(OHMe)4][PhTm(Me)] has been determined. The syntheses and characterization of complexes [M(PhTm(Me))(PR3)] (M = Cu, Ag, Au; R = Et, Ph;) are reported, and the complexes [Cu(PhTm(Me))(PPh3)], [Ag(PhTm(Me))(PEt3)] and [Au(PhTm(Me))(PEt3)] are crystallographically characterized, showing a progression from pseudo-tetrahedral geometry (copper, S3P coordination) to trigonal planar geometry (silver, S2P coordination) to linear geometry (gold, SP coordination). In addition, the copper(I) and silver(I) triphenylphosphine complexes of the adventitiously formed phenylhydrobis(methimazolyl)borate ligand, [M(PhBm(Me))(PPh3)], have been crystallographically characterized, showing both species to have a trigonal planar primary coordination sphere, with a secondary M...H-B interaction. Finally, reaction of copper(II) chloride with Li[PhTm(Me)] results in formation of a compound analyzing as [Cu(II)(PhTm(Me))Cl], although its extreme insolubility and marked instability have precluded its complete characterization. Attempts to prepare this by ultra-slow diffusion of the reactants through solvent blanks has led to isolation of a mixed-valence copper(I/II) methimazolate cluster, [Cu(I)10Cu(II)2(mt)12Cl2] and a copper(I) dimeric complex [Cu2(PhTm(Me))2], indicating that copper(II) ions oxidatively decompose the phenyltris(methimazolyl)borate anion.     

Coordination chemistry of novel scorpionate ligands based on 3-cyclohexylpyrazole and 3-cyclohexyl-4-bromopyrazole

The ligands [hydrotris(3-cyclohexylpyrazol-1-yl)borate, [Tp(Cy)](-), tetrakis(3-cyclohexylpyrazol-1-yl)borate, [pz(o)Tp(Cy)](-), and hydrotris(3-cyclohexyl-4-bromopyrazol-1-yl)borate, [Tp(Cy,4Br)](-) were synthesized and characterized as their Tl(I) derivatives. They were converted to a variety of tetrahedral LMX and octahedral LML' complexes, as well as to the dinuclear nickel carbonate complex [Ni(Tp(Cy))](2)(CO(3)), 4, and the compound Ni[Tp(Cy,4Br)][pz(Cy,4Br)](3)(H)(2), 5. The structures of Co[Tp(Cy)]Cl, 1, Co[Tp(Cy,4Br)]Cl, 2, Co[Tp(Cy,4Br)]NCS, 3, [Ni(Tp(Cy))](2)(CO(3)), 4, Ni[Tp(Cy,4Br)][pz(Cy,4Br)](3)(H)(2), 5, and Mo[Tp(Cy)](CO)(2)(eta(3)-methallyl), 6, were determined by X-ray crystallography. The structures of paramagnetic heteroleptic complexes Co[Tp(Cy)][Tp], Co[Tp(Cy)][Tp], Co[Tp(Cy,4Br)][Tp], and Co[Tp(Cy,4Br)][Tp] were established by NMR. The homoleptic compounds Co[Tp(Cy)](2) and Co[Tp(Cy,4Br)](2) rearrange thermally to Co[Tp(Cy)](2) and to Co[Tp((Cy,4Br))](2), respectively, containing one 5-cyclohexyl group/ligand.     

Non-contact dilatometry of hard and soft porcelain compositions

Two different porcelain compositions were studied: a soft and a hard one. DTA, optical non-contact dilatometry and DSC were used to evaluate the thermal behaviour of the porcelain compositions with the aim to master the suitable thermal cycle for each. Results were interpreted on the basis of mineralogy and microstructure: the amorphous phase, abundant in soft porcelain, plays an important role on thermal expansion (8·10^–6 K^–1 for soft and 6·10^–6 K^–1 for hard at 1000°C). Thermal expansion behaviour as function of firing time was also studied. Non-contact dilatometry characterisation of porcelain bodies enable to master the suitable thermal cycle for the sintering.     

Further links between the maximum hardness principle and the hard/soft acid/base principle: insights from hard/soft exchange reactions

Ayers, Parr, and Pearson recently showed that insight into the hard/soft acid/base (HSAB) principle could be obtained by analyzing the energy of reactions in hard/soft exchange reactions, i.e., reactions in which a soft acid replaces a hard acid or a soft base replaces a hard base [J. Chem. Phys., 2006, 124, 194107]. We show, in accord with the maximum hardness principle, that the hardness increases for favorable hard/soft exchange reactions and decreases when the HSAB principle indicates that hard/soft exchange reactions are unfavorable. This extends the previous work of the authors, which treated only the "double hard/soft exchange" reaction [P. K. Chattaraj and P. W. Ayers, J. Chem. Phys., 2005, 123, 086101]. We also discuss two different approaches to computing the hardness of molecules from the hardness of the composing fragments, and explain how the results differ. In the present context, it seems that the arithmetic mean of fragment softnesses is the preferable definition.     

Lower main-group element complexes with a soft scorpionate ligand: the structural influence of stereochemically active lone pairs

The syntheses and structures of complexes of the fifth period elements indium and antimony, and the sixth period element bismuth with the soft scorpionate ligand, hydrotris(methimazolyl)borate (Tm(Me)) are reported. A considerable variety of structural motifs were obtained by reaction of the main-group element halide and NaTm(Me). The indium(III) complexes took the form [In(kappa(3)-Tm(Me))(2)](+). This motif could not, however, be isolated for antimony(III), the dominant product being [Sb(kappa(3)-Tm(Me))(kappa(1)-Tm(Me))X] (X = Br, I). An iodo-bridged species [Sb(kappa(3)-Tm(Me))I(mu(2)-I)](2), analogous to a previously reported bismuth complex, was also isolated. Reaction of antimony(III) acetate with NaTm(Me) results in a remarkable species in which three different ligand binding modes are observed. In each antimony complex the influence of the nonbonded electron pair is observed in the structure. Bismuth halides form complexes analogous to those of antimony, with directional lone pairs, but in addition, reaction of Bi(NO(3))(3) with NaTm(Me) results in a complex with a regular S(6) coordination sphere and a nonstereochemically active lone pair. Comparisons are drawn with known Tm(Me) complexes of As, Sn, and Bi in which the stereochemical influence of the lone pairs is negligible and with Tm(Me) complexes of Te and Bi in which the lone pairs are stereochemically active. This study highlights the ability of Tm(Me) to coordinate in a variety of modes as dictated by the metal centre with no adverse effects on the stability of the complexes formed.     

New synthetic and structural aspects in the chemistry of alkylaluminum fluorides. The mutual influence of hard and soft ligands and the hybridization as rigorous structural criterion

A general synthetic strategy starting from metal alkyls is reported based on the hydrogen difluoride anion as a suitable reagent for obtaining organometallic fluorides. The newly prepared compounds are [Me(4)N][(i-Bu)(2)AlF(2)] (1), [Ph(4)P][(i-Bu)(2)AlF(2)] (2), and [Ph(4)P][AlF(4)] (3), containing the tetrahedral anions [(i-Bu)(2)AlF(2)](-) and [AlF(4)](-). The actual structures are prototypes that allowed a comparison of inorganic and organometallic fluorides in the frame of the hard and soft acid and base principle, by means of ab initio calculations. A new theoretical model is designed to put in equation form the qualitative statements of the Bent rule. The model allows the rationalization of the tendencies of bond angle variation in [R(2)MX(2)] systems containing a main group metal (M), in terms of hybridization of the central atom and the reciprocal influence of hard and soft ligands.     

Combining hard and soft donors in early-transition-metal olefin polymerization catalysts

Bis(phosphanylphenoxide) complexes of the group 4 metals, upon activation by methylaluminoxane, are highly active for ethylene and propylene polymerization; a zirconium derivative possesses one of the highest propylene polymerization activities found to date for a nonmetallocene system.     

Electronic aspect of the HSAB principle (hard and soft acids and bases)

Using the quantum mechanical SCF MO LCAO and SCF X-SW methods, we have shown the effect of the hard and soft acids and bases principle in a new aspect: Inversion of the metal halides series BX₃ and AlX₃ (X=F, Cl, Br) on going from N- to P- and from O- to S-containing bases. We have analyzed the electronic nature of the differences in the systems NH₃, PH₃ and OH₂, SH₂ responsible for the inversion of the acid series.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 75–78, January–February, 1986.     

Soft scorpionate complexes of the fourth and fifth period elements arsenic and tin

We report the synthesis and structure of arsenic (III) and tin(IV) adducts of the hydrotris(methimazolyl)borate anion (Tm^Me). Both species are found to be [E(κ³Tm^Me)₂]ⁿ⁺ anions (E=As, n=1; E=Sn, n=2). Comparisons are made between each of these species and the compounds formed with their heavier and larger group partners bismuth and lead. Due to the remarkable flexibility in the soft scorpionate ligand we were unable to form a charge-separated species analogous to that reported by Parkin for the phenyl analogue (Tm^Ph). Attempts to prepare the tin(II) adduct curiously produced the tin(IV) product [Sn(κ³Tm^Me)₂][Tm^Me]₂ even when the reaction was carried out under inert atmospheres.     

Functional materials: from hard to soft porous frameworks

This Review aims to give an overview of recent research in the area of porous, organic-inorganic and purely organic, functional materials. Possibilities for introducing organic groups that exhibit chemical and/or physical functions into porous materials will be described, with a focus on the incorporation of such functional groups as a supporting part of the pore walls. The number of organic groups in the network can be increased such that porous, purely organic materials are obtained.     

Monitoring alcoholic fermentation by joint use of soft and hard modelling methods

The strengths of hard and soft modelling were exploited by using both types of methods in combination to monitor alcoholic fermentations under Saccharomyces cerevisiae yeasts. Experimental work was performed in two steps. In the first, fermentation processes were conducted under identical conditions except for the initial glucose concentration in order to tests various previously reported empirical hard modelling methods. The product inhibition model of Hinshelwood was found to provide the best results in terms of goodness of fit and consistency in parameter values between runs under these conditions. In the second step, fermentation processes conducted at variable temperature and pH were monitored in-line by using an immersion NIR probe. The results were processed by using multivariate curve resolution-alternating least-squares (MCR-ALS) methodology in combination with the hard modelling information obtained in the first step as spectral equality constraints. Notwithstanding the complexity of the fermentation matrix introduced by variability in the species involved in yeast metabolism, the extracted profiles exhibited highly significant correlation with the reference values provided by a validated reference method for the determination of glucose, ethanol and biomass. The results testify to the efficiency of the joint use of soft and empirical hard modelling for studying evolving biological systems and opens up new avenues for application to other bioprocesses.     

Synthesis of nanostructured iron titanates by soft chemistry methods

The efficiency of various methods for the preparation of titania-based nanocomposites, Fe₂Ti₂O₇ and Fe₂TiO₅, starting from colloid solutions of hydroxy iron species and the products of titanium tetraisopropoxide hydrolysis was evaluated. The effect of the conditions of synthesis (Fe³⁺/Ti⁴⁺ concentration ratios of 1 and 2, pH of the reaction medium, temperature, and sonication) on the composition, structure, and properties of the nanocomposites formed was elucidated; the effect of the phase composition on the photocatalytic activity of materials formed during the liquid-phase synthesis was established. The resulting materials were studied by electron microscopy, low-temperature adsorption, IR spectroscopy, and powder X-ray diffraction.     

Nanorods of cryptomelane via soft chemistry method and their catalytic activity

α-MnO₂ nanorods were obtained by a fast redox transformation of aqueous solution of potassium permanganate. The formation mechanism of 1D nanocrystals proceeds via a first pH- and temperature sensitive stage followed by cation/anion control of the nanorod growth. A high surface area and nanostructuring allowed to achieve superb catalytic activity in a CO oxidation process compared to a conventionally prepared manganese dioxide.     

Studies of australian soft corals—XXXV : The terpenoid chemistry of soft corals and its implications

The in vivo incorporation of mevalonolactone specifically into the terpene portion of a sesquiterpene hydroquinone is reported for the soft coral Sinularia capillosa Eudesma-4 , 7(11)-diene-8β-ol (20) and the corresponding 8-keto derivative (21) have been isolated from the soft coral Nephthea species for the first time The aeolid nudibranch Phyllodesmium longicirra was collected when feeding on the soft coral Sarcophyton trocheliophorum and the known diterpene trocheliophorol (25) was found to be concentrated in the cerata of the nudibranch. The absolute stereochemistry of trocheliophorol (25) has been rigorously determined, and shown to be that previously assigned on spectroscopic grounds     

Reactivity of the tetrathiomolybdate(VI) anion towards hard and soft base chelating agents

Summary The interaction of hard base chelating agents (LH) such as 8-quinolinol (oxH), salicylaldehyde (salH) andN-nitrosophenylhydroxylamine (NphaH) with ammonium tetrathiomolybdate(VI), (1), in aqueous solution yields disulphidomolybdenum(VI) complexes, [MoS₂L₂]. The i.r. absorptions at 540 and 510 cm^–1 are assigned tov(Mo-S), which indicate that the two sulphido-groups arecis to each other, The interaction of (1) with soft base chelating agents (SS), such as dithiocarbamates (dtc), dithiophosphate (dtp) and xanthates (xan) yields dimeric sulphido-bridged sulphidomolybdenum(V) complexes, [Mo₂S₄(SS)₂] and with potassium ethylthioxanthate (KEttxan) yields a molybdenum(IV) complex, [Mo(Ettxan)₄]. The [Mo₂S₄(R₂dtc)₂] complexes were also obtained by the interaction of [MoO₂(R₂dtc)₂] with phosphorus pentasulphide in xylene. It was concluded that tetrathiomolybdate(VI) undergoes facile reduction when compared with tetraoxomolybdate(VI).