Lewis base complex

Several alternative attempts have been made to quantify Lewis-acid Lewis-base interaction. In view of the HSAB theory, the applicability of a scale which describes Lewis acidity with only one parameter will be unavoidably restricted to a narrow range of struchirally related Lewis bases. The use of more than one parameter results in relationships with a more general validity ". However, a quantitative prediction of the gas-phase stabilities of Lewis-acid Lewis-base complexes is still difficult. Hence the interpretation, not to mention the prediction, of solvent effects on Lewis-add Lewis-base interactions remains largely speculative. 

Boron tnfluonde etherate (Lewis acid Lewis base complex)... 

The product of this reaction a Lewis acid Lewis base complex called informally boron tnfluonde etherate may look unusual but it is a stable species with properties different from those of the reactants Its boiling point (126°C) for example is much higher than that of boron tnfluonde—a gas with a boiling point of — 100°C—and diethyl ether a liquid that boils at 34°C... 

Iron(III) bromide is a weak Lewis acid It combines with bromine to form a Lewis acid Lewis base complex... 

Their polar carbon-oxygen bonds and the presence of unshared electron pairs at oxygen contribute to the ability of ethers to form Lewis acid Lewis base complexes with metal ions... 

The metal-ion complexmg properties of crown ethers are clearly evident m their effects on the solubility and reactivity of ionic compounds m nonpolar media Potassium fluoride (KF) is ionic and practically insoluble m benzene alone but dissolves m it when 18 crown 6 is present This happens because of the electron distribution of 18 crown 6 as shown m Figure 16 2a The electrostatic potential surface consists of essentially two regions an electron rich interior associated with the oxygens and a hydrocarbon like exterior associated with the CH2 groups When KF is added to a solution of 18 crown 6 m benzene potassium ion (K ) interacts with the oxygens of the crown ether to form a Lewis acid Lewis base complex As can be seen m the space filling model of this... 

Ethers form Lewis acid Lewis base complexes with metal ions Certain cyclic polyethers called crown ethers, are particularly effective m coor dinatmg with Na" and K" and salts of these cations can be dissolved m nonpolar solvents when crown ethers are present Under these conditions the rates of many reactions that involve anions are accelerated... 

Free borane (2) exists as gaseous dimer—the diborane BaHg. In addition Lewis acid/Lewis base-complexes, as for example formed in an ethereal solvent, e.g. 4, are commercially available ... 

In reaction with an alkene, initially a three-membered ring Lewis acid/Lewis base-complex 5 is formed, where the carbon-carbon double bond donates r-electron density into the empty p-orbital of the boron center. This step resembles the formation of a bromonium ion in the electrophilic addition of bromine to an alkene ... 

Lewis Base complexes—Group V donor atoms... 

Bifunctional Asymmetric Catalysis Promoted by Chiral Lewis Acid -Lewis Base Complexes... 

Interestingly, homolytic substitution at boron does not proceed with carbon centered radicals [8]. However, many different types of heteroatom centered radicals, for example alkoxyl radicals, react efficiently with the organoboranes (Scheme 2). This difference in reactivity is caused by the Lewis base character of the heteroatom centered radicals. Indeed, the first step of the homolytic substitution is the formation of a Lewis acid-Lewis base complex between the borane and the radical. This complex can then undergo a -fragmentation leading to the alkyl radical. This process is of particular interest for the development of radical chain reactions. 

Intramolecular Lewis base complexation of the germanium atom also did not appear to be a valuable alternative to overcome the lability of these elusive intermediates, since the germanones expected from oxidation of the base-stabilized germylenes 140131 (with Me3NO) and 141132 (with 02, DMSO, or pyridine oxide) either rearrange as already mentioned [Section VI,A,4, Eq. (33)]131 or dimerize to digermadioxetane 160132 [Eq. (35)]. 

If doubly-bonded compounds >M = X (M = Si, Ge, Sn) are now well known, this is not yet the case for the heavy allenic derivatives >M = C = X. Transient silaallenes >Si = C = C 160-167 or silaazaallene >Si = C = N—168 were postulated some years ago, but the first stable derivative of this type, a formal 3-stanna-l-azaallene >Sn = C = N —, was isolated only in 1992 by Griitzmacher et al169 The compound Tbt(Mes)Si = C = NR170 has also been obtained, but according to the authors it is closer to a silylene Lewis base complex than to a silacumulene. The first stable silaallene was only reported in 1993 by West et al.111 and the first metastable >Si = C = P— was characterized still more recently.172... 

C. Reduction Potentials of Lewis Base Complexes and the Calculation of Dissociation Constants for the Fe(II) Complexes... 

Lewis Base Complexes, Chelated Metal Amides and Heteroleptic Amido Complexes... 

II. Theoretical Studies of Silylene-Lewis Base Complexes. 2... 

---