Lewis bases pyridine

The addition of a Lewis base (pyridine) did not significantly alter the polymerization rate in THF, although a small increase in rate was observed in toluene,... 

The carbazole compounds, (77 -Af-carbazolyl)2Ca(pyridine)4, (Tj -N-car-bazolyl)2Sr(NH3)(DME)2, and (i7 -Af-carbazolyl)2Ba(DME)3 (Fig. 9), are colorless or yellow solids that have good solubility in donor solvents such as pyridine. They are monomeric in the solid state with the carbazolyl ligands bonded only through the nitrogen atom (tj ) to the metals. The metal coordination spheres are completed by incorporation of the Lewis bases pyridine, DME, and ammonia. A smooth increase in coordination number with metal size, from 6 (Ca) to 7 (Sr) to 8 (Ba), is observed in these compounds. The reason for the Tj -Af-bondingof the carbazolyl ligand instead of multihapto bonding as occurs in the alkali metal compounds of carbazole and the fluorenyl compounds of the alkaline-earth metals (see Section III,G,2) is presently unclear. ... 

The results in Table 1 indicate that the surface characteristics of these silicon nitride powders are different from one another. For example, the as-received powder was the only one that reacted weakly with Lewis base pyridine and ketones. On the other hand, all silicon nitrides except the air heat-treated one have similar elution terrrperatures for straight dliphatics this implies a change of surface activity n le to oxidization. The differences of the powder surfaces treated with Ar-4% H2. N2-4% H2, or N2 are real but subtle. The N2-treated powder Is moie polar and acidic than the other two. showing stronger Interaction with polarizable compounds (benzene, toluene. and xylene) and with Lewis base ether. 

It is isoelectronic and isostmctural with the aluminum sandwich ion [i (9y y (9-3,3 -Al(3,l,2-AlC2B2H22)2]A shown iu Figure 26a. TThe siUcon is Tj -bonded iu unshpped fashion to the C2B2 faces of two dicarboUide cages. TThis bis-dicarboUide sUicon sandwich also forms adducts of a variety of stmctural types with Lewis bases such as pyridine and trimethylphosphine. 

The reaction of CF3I and CgFjI with dialkylzmc in the presence of a Lewis base, such as diglyme or pyridine, quantitatively gives the corresponding fluori-nated organozinc complexes [32] (equation 23) When Rf is C2F5 or iso CjF-j, the pure zinc complexes are not isolated... 

A1C13, or S02 in an inert solvent cause colour changes in indicators similar to those produced by hydrochloric acid, and these changes are reversed by bases so that titrations can be carried out. Compounds of the type of BF3 are usually described as Lewis acids or electron acceptors. The Lewis bases (e.g. ammonia, pyridine) are virtually identical with the Bransted-Lowry bases. The great disadvantage of the Lewis definition of acids is that, unlike proton-transfer reactions, it is incapable of general quantitative treatment. 

The 14e compound MTO readily forms coordination complexes of the type MTO-L and MTO-L2 with anionic and uncharged Lewis bases [96], These yellow adducts are typically five- or six-coordinate complexes, and the Re-L system is highly labile. Apart from their fast hydrolysis in wet solvents, MTO-L adducts are much less thermally stable then MTO itself. The pyridine adduct of MTO, for instance, decomposes even at room temperature. In solution, methyltrioxorhenium displays high stability in acidic aqueous media, although its decomposition is strongly accelerated at increased hydroxide concentrations [97, 98], Thus, under basic aqueous conditions MTO decomposes as shown in Equation (4). 

Cyan-chinolin ergibt in Pyridin, das als Lewis-Base mit starken komplexbildenden Higcnschaften die Hete-rolyse der C C-Bindung fordert, 25% d.Th. Chinolin neben 6% d.Th. 1,2,3,4-Tetrahydro-chinolin2. 

Complexes of molybdenum in the lower valence-states of -t 2 and + 3 have been produced only in the past two years. For the Mo(II) species, the usual starting-material is Mo2(acetate>4. Reaction of this with KS2COEt in THF gives two products, a green complex tentatively assigned as [Mo2(Etxant>4], which solvates to form the red complex [Mo2(Etxant)4(THF)2]. The structure of the latter complex was elucidated by X-ray analysis 169). Steele and Stephenson 170) were also able to synthesize a red, crystalline solid (methanol solution), which they formulated as [Mo(Etxant)2]2 (XI), and reacted this with Lewis bases, e.g., pyridine, to form [Mo(Etxant)2L]2- Thus, there appears to be a difference between the two compounds formulated as [Mo2(Et-xant)2]2 that... 

While our discussion will mainly focus on sifica, other oxide materials can also be used, and they need to be characterized with the same rigorous approach. For example, in the case of meso- and microporous materials such as zeolites, SBA-15, or MCM materials, the pore size, pore distribution, surface composition, and the inner and outer surface areas need to be measured since they can affect the grafting step (and the chemistry thereafter) [5-7]. Some oxides such as alumina or silica-alumina contain Lewis acid centres/sites, which can also participate in the reactivity of the support and the grafted species. These sites need to be characterized and quantified this is typically carried out by using molecular probes (Lewis bases) such as pyridine [8,9],... 

Host-guest complexes such as (67) have been prepared from molecular squares involving Lewis base receptor sites, such as cyclobis[(cw-(dppp)Pt(4-ethynylpyridyl)2)(cM-LM)]Ag2 6+(OTf)6, where M = Pdn or Ptn and L = dppp or 2PEt3, by reaction with pyridine, pyrazine, phenazine, or 4,4 -dipyridyl ketone.519... 

We have shown that pyridine forms stable complexes with Zr(benzyl)4, and that ethers may also coordinate in a similar way. Pyridine, ethers, and olefins may be considered as a class of Lewis bases, the strength of which is determined by the position of the equilibrium ... 

Reversible pyridine dissociation yields the non-Lewis base stabilized imido complex [Cp(NHAr) Ti=NAr] (54). This coordinatively unsaturated species undergoes a [2 + 2] cycloaddition reaction with allene to give an azatitanocyclobutane (55), which is then protonated to the /mamido complex. Elimination of enamine occurs followed by isomerization to the energetically more favorable imine. 

As has already been mentioned, boron halides are electron-deficient molecules. As a result, they tend to act as strong Lewis acids by accepting electron pairs from many types of Lewis bases to form stable acid-base adducts. Electron donors such as ammonia, pyridine, amines, ethers, and many other types of compounds form stable adducts. In behaving as strong Lewis acids, the boron halides act as acid catalysts for several important types of organic reactions (see Chapter 9). 

The chemistry of coordination compounds comprises an area of chemistry that spans the entire spectrum from theoretical work on bonding to the synthesis of organometallic compounds. The essential feature of coordination compounds is that they involve coordinate bonds between Lewis acids and bases. Metal atoms or ions function as the Lewis acids, and the range of Lewis bases (electron pair donors) can include almost any species that has one or more unshared pairs of electrons. Electron pair donors include neutral molecules such as H20, NH3, CO, phosphines, pyridine, N2, 02, H2, and ethyl-enediamine, (H2NCH2CH2NH2). Most anions, such as OH-, Cl-, C2042-, and 11, contain unshared pairs of electrons that can be donated to Lewis acids to form coordinate bonds. The scope of coordination chemistry is indeed very broad and interdisciplinary. 

This preparation is carried out in an aprotic solvent (e.g. benzene, chloroform) with no special provision other than working in a well-ventilated fume hood to avoid ill-smelling sulfur compounds. Various ligands have proved successful phosphines, pyridines, imidazoles, tetra-m ethyl thiourea, etc. When the same reaction is carried out in the absence of the Lewis base L, a dimer 6 is obtained, which is a useful catalyst in its own right and sometimes a much more active one see Section VILA. The chemical equation for that reaction is,... 

We conclude that only one phosphine attacks a ji-S group of 20. Indeed, the phosphine sulfide product from dmpm is Me2P(S)CH2PMe2, not a bis(sulfide).The other phosphine implicated by Eqs. (32) and (33), whether from a second PR3 or from a di-phosphine, adds as a Lewis base to rhenium. The basis for this is that a pyridine easily replaced one of the phosphines in the mechanism. This proposed mechanism should steer the reaction directly towards formation of 21, but owing to the dilemma posed in point (c), an intermediate likely intervenes. It can partition to the slowly-reacting 21 or to 23, the latter step requiring additional phosphine Scheme 13 shows the postulated mechanism. The dual role for phosphine and the use of Py in its place and the proposal for partitioning are shown in Scheme 14. 

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