Lewis adduct

I. Our Starting Point Conformational Analysis of Lewis Adducts... 

Having worked for many years on chemistry and the behavior of Lewis adducts in nonmetallic coordination chemistry, we realized in 1970 that conformational analysis, both experimental and theoretical, of such compounds needed to be developed. 

Such work could be used to test the validity of a quantum approach to preferred conformations of Lewis adducts. We therefore decided to perform such a test by means of semi-empirical methods in the hope of providing chemists with an inexpensive, rapid, reliable tool for the study of large series of compounds. 

We concluded that a CNDO/2 approach could help us not only to reproduce conformational observables but also to understand the origin of preferred conformations and of any related parameter. Clearly, this facility must be connected with the fact that Lewis adducts or, more generally, inorganic compounds can be qualified as electronically localized systems. The existence of a clearly defined field of potential applications was simultaneously demonstrated by Gropen and Seip (9) and Perahia and Pullman (10). 

Within the field of Lewis adducts, we naturally studied the conformational analysis of the parent borazane complex, H3N BH3, and of its fluorinated derivatives (13) and showed that, with respect to their preferred conformation, there is no determinant AEN-.iH spatial term analogous to the AEP...H term discussed above relative to F3P BH3. 

This investigation revealed a basic discrepancy between Lewis adducts containing only atoms from the first row of the periodic table and those containing at least one atom from the second row. We therefore initiated a critical examination of the M(CH3)2 (14) and M(CH3)3 (75) series in which M could be either a first-row element (CH2, NH, 0 or CH, N) or a second-row element (SiH2, PH, S orSiH,P). 

We have combined this kind of work with electron diffraction on many occasions. Let us mention the example of the Cl3 A1 NH3 Lewis adduct we studied withM and I. Hargittai (Budapest) and V. P. Spiridonov (Moscow) (39). 

We had been working with Lewis adducts for many years, so that the prediction of the basic properties of bases with respect to a given Lewis acid was extremely... 

The double-scale four-parameter enthalpic equation proposed in 1965 (54) and successfully developed by Drago et al seems to be the best tool so far available for correlating and predicting the formation enthalpies of Lewis adducts in the gas phase or, if really necessary, in solution. 

In concluding this section, we wish to emphasize that extreme care is necessary when predicting the basicity of donor molecules from experimental or theoretical studies performed on these molecules in their free state. Such an approach appears to be correct when the acceptor moiety is H+ but may lead to error as the Lewis adduct becomes bulkier, since its volume induces dramatic conformational changes with... 

The tendency for a Br0nsted acid to act as a proton donor, expressed in terms of the compound s dissociation constant in water. 2. The term also refers to the tendency to form a Lewis adduct, as measured by a dissociation constant. 

A thermodynamic measure of the proton-donating or proton-accepting ability of a solvent system (or closely related thermodynamic property such as the ability of a solvent system to form Lewis adducts) ". ... 

The thermodynamic tendency of a substance to act as a Lewis acid. The strength of a Lewis acid depends on the nature of the base with which the Lewis acid forms a Lewis adduct. Hence, comparative measures of Lewis acidities are given by equilibrium constants for the formation of the adducts by a common reference base. See Lewis Acid Electrophilicity Hard Acids Soft Acids Acceptor Number... 

Any chemical species that can donate a pair of electrons to a Lewis acid to form a Lewis adduct. Examples of Lewis bases include NH3, RNH2, ROH, CO, COs and RSH. See Lewis Acid... 

A cyclohexadienyl Lewis adduct or salt formed by the reaction of a Lewis base with an aromatic compound. Such an adduct is apparently formed from the reaction of OH with 4-(A/-2-aminoethyl-2 -pyridyl disulfide)- -nitrobenzo-2-oxa-l,3-diazole (2PROD). 2PROD is a two-protonic-state electrophile used as a probe for enzyme active site nucleophiles and as a fluorescent re-... 

Catalysis by a Lewis base in which a Lewis adduct is a reaction intermediate. 

FEEDBACK INHIBITION ADDITIVITY PRINCIPLE ADDUCT COMPLEX LEWIS ADDUCT MEISENHEIMER ADDUCT Adenine,... 

DEGREE OF DISSOCIATION LEWIS ACIDITY ACCEPTOR NUMBER ELECTROPHILICITY HARD ACID LEWIS ACID LEWIS BASE LEWIS BASICITY SOFT ACID Lewis adduct,... 

The ability of the boron atom of 59 to engage in a donor-acceptor interaction was illustrated with DMAP and DABCO (DABCO = diazabi-cyclo-[2.2.2]-octane) that readily formed the corresponding Lewis adducts. Interestingly, a similar behavior was retained after coordination of the phosphorus atom to palladium. The formation of the Lewis base adducts 66a and 66b of complex 65 (Scheme 38) was supported by solid-state 31P and nB CP/MAS-NMR spectroscopy (<5 1 B = 5-6 ppm), although the occurrence of decomposition and/or dissociation processes impeded spectroscopic characterization in solution and recrystallization to obtain X-ray quality crystals. Compounds 66a and 66b substantiate the ability of ambiphilic compounds to engage concomitantly into the coordination of donor and acceptor moieties. Such a dual behavior opens interesting perspectives for the preparation of metallo-polymers and multimetallic complexes. 

Electron-donor-acceptor complex — A term sometimes employed instead of charge-transfer complex or Lewis adduct. See also quinhydrone. 

Enantiomerically pure phosphines are frequently employed as ligands in transition-metal-catalyzed asymmetric reactions. For this reason, various methods have been designed for their preparation.1 Many of them involve the use of borane adducts of trivalent phosphorus compounds,2 in which the borane moiety mainly acts as a protecting group. These Lewis adducts are easily prepared and stable to air, and several methods have been designed to cleave them. 

D. HABj.—Although several molecules of this general formulae have been studied earlier, only two papers which deal with the Lewis adducts of BH3 and BF3 are referred to here. 

This is a general term that, whenever appropriate, should be used in preference to the less explicit term complex. It is also used specifically for products of an addition reaction. For examples, see jt-adduct, Lewis adduct, and Meisenheimer adduct. 

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