Oxidative Addition of Nonpolar Reagents

Oxidative addition of nonpolar reagents requires a site of unsaturation and a d-electron count of 16 or less. 

Table 6.2. Estimates of the enthalpy and free energy for oxidative addition of several nonpolar and polar reagents.

The remainder of this chapter presents the reactions of nonpolar reagents with a range of metals. The reactions of dihydrogen are presented first the reactions of silanes are presented second because they often react like dihydrogen. The additions of C-H bonds are presented third examples of intramolecular additions of C-H bonds are presented before intermolecular examples. This chapter closes with a discussion of the oxidative addition of C-C bonds. 

In contrast to the rare occurrence of the oxidative addition of C-C bonds, the oxidative addition of the nonpolar bonds between two main group atoms, such as boron and silicon, can be facile. The oxidative addition of Si-Si bonds in disilanes and the B-B bond in diborane(4) reagents is likely to be a step in a variety of catalytic reactions, including the additions of disilanes, - diborane(4) reagents, and silaboranes - across olefins and alkynes, the silylation and borylation of arene C-H bonds, - - the borylation of alkane C-H bonds, and the conversion of aryl halides to arylsilanes and arylbo-ronate esters. " ... 

Oxidative additions of substrates containing H-X bonds that are more polar than those in a hydrocarbon, silane, or borane have been studied recently. These reactions can occur through a pathway involving a three-centered transition state, or they can occur by protonation of a basic metal center. The latter pathway requires a highly acidic reagent when the reactions are conducted in nonpolar media that do not stabilize charged intermediates. 

The addition of the phosphine oxide anion to the carbonyl is dramatically affected by solvent, base and temperature. These conditions can be modified in order to maximize the erythro isomer formation. In nonpolar solvents the addition proceeds with virtually no selectivity. Substantial improvements are seen by Ae use of ethers, and the highest ratios of erythro adduct (225) are obtained in THF with the lithium complexing reagent TMEDA present at -78 C or lower temperatures (equation S6). 

Both O-alkyl hydroxylamines and, especially, arylhydrazines, are slightly oxidized compounds. The presence of any oxidizers in the reaction mixtures must be excluded. Nevertheless, in real practice, these mixtures very often contain some by-products (e.g., ArNH2, ArOH, ArH, etc.). Usually, there are no problems to reveal their chromatographic peaks, because aU of them have lower retention parameters than those for the initial reagents and, moreover, all target derivatives. The condensation reaction of the considered type can be characterized by statistically processed differences of retention indices of products and initial substrates. This mode of additive scheme permits us to estimate these analytical parameters for any new derivatives on standard nonpolar polydimethyl siloxanes. For the simplest reaction scheme, Ah— —>Bh—, AMW = MW(B) -MW(A) and ARl, = RI(B) RI(A) ... 

Novel lanthanide fi-diketonate complexes have been synthesized, Their properties include thermal, hydrolytic and oxidative stabilities, volatility, Lewis acidity, and unusually high solubility in nonpolar organic solvents. Various combinations of these properties make lanthanide complexes useful as NMR shift reagents and fuel antiknock additives and in other applications. NMR spectral studies revealed that the Pr(III), Yb(III), and Eu(III) complexes of 1,1,1,2,2,3,3,7,7,7- decafluoro-4,6-heptanedione have sufficient Lewis acidity to induce appreciable shifts in the proton resonances of weak Lewis bases such as anisole, acetonitrile, nitromethane, and p-nitrotoluene. Data from single-crystal structure determinations indicate that the NMR shift reagent-substrate complexes are not stereochemically rigid and that effective axial symmetry may exist by virtue of rapid intramolecular rearrangements. 

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