Alkoxides and Aryloxides

Complexes LnM3tris(binapthoxide) (M = alkali metal) have a good deal of utility as catalysts. 

The lanthanide complexes are soluble in ethers like Et20 or THE. They are catalysts for the enantioselective reduction of aldehydes, with best results for the lanthanum complex. Thus the yield is 72% when M = La, but 50% when M = Yb more strikingly, the enantiomeric excess is 69% for the La complex but only 3% when the Yb complex was 

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The general formula for boric acid esters is B(OR)2. The lower molecular weight esters such as methyl, ethyl, and phenyl are most commonly referred to as methyl borate [121 -43-7] ethyl borate [130-46-9J, and phenyl borate [1095-03-0] respectively. Some of the most common boric acid esters used in industrial appHcations are Hsted in Table 1. The nomenclature in the boric acid ester series can be confusing. The lUPAC committee on boron chemistry has suggested using trialkoxy- and triaryloxyboranes (5) for compounds usually referred to as boric acid esters, trialkyl (or aryl) borates, trialkyl (or aryl) orthoborates, alkyl (or aryl) borates, alkyl (or aryl) orthoborates, and in the older Hterature as boron alkoxides and aryloxides. CycHc boric acid esters, which are trimeric derivatives of metaboric acid (HBO2), are known as boroxines (1). 

The alkoxides and aryloxides, particularly of yttrium have excited recent interest. This is because of their potential use in the production of electronic and ceramic materials,in particular high temperature superconductors, by the deposition of pure oxides (metallo-organic chemical vapour deposition, MOCVD). They are moisture sensitive but mostly polymeric and involatile and so attempts have been made to inhibit polymerization and produce the required volatility by using bulky alkoxide ligands. M(OR)3, R = 2,6-di-terr-butyl-4-methylphenoxide, are indeed 3-coordinate (pyramidal) monomers but still not sufficiently volatile. More success has been achieved with fluorinated alkoxides, prepared by reacting the parent alcohols with the metal tris-(bis-trimethylsilylamides) ... 

Metal-Oxygen Bond Lengths, M—O—C Angles, and Torsion Angles for Three-Coordinate Aluminum and Gallium Alkoxides and Aryloxides... 

Zinc alkoxide and aryloxide complexes have been of particular interest as enzyme models and catalysts. Tetrameric alkyl zinc alkoxides are a common structurally characterized motif.81... 

Overall, the alkali metal alkoxide and aryloxide systems are excellent examples in demonstrating the effects of steric influences on both molecular aggregation and also on the nature of any extended network architecture adopted. The large database of O-M complexes that have now been identified has led to a good deal of predictability regarding the coordination chemistry of these species. 

In THF, monomeric RMgX (I) and R2Mg (II) co-exist over a wide concentration range for the chlorides, bromides and iodides. The fluorides are present as the F-bridged dimers across the whole concentration range. Similarly, the alkoxide and aryloxide compounds, RMgOR, are present as the R2Mg(/r-OR )2Mg species in THF. 

TABLE 8. Selected H and NMR data for magnesium alkoxide and aryloxide compounds... 

TABLE 4. Structurally characterized organomagnesium alkoxides and aryloxides, showing their methods of preparation... 

Organomagnesium alkoxides and aryloxides have been utilized in only a few applications. Methyhnagnesium f-butoxide 68 has been used in the chemical vapor deposition of MgO films onto silicon substrates . MgO films with good crystallinity were grown at 800 °C on Si(lll) surfaces, whereas polycrystalline films were formed at 400 °C. Intermediate temperatures produced multiple crystallite orientations. Similar results were obtained for deposition onto Si(lOO) surfaces over this range of temperatures. 

Compounds 134, 135 and 136 (Figure 71) are aUcylzinc alkoxides and aryloxides that exist as discrete monomeric molecules in the solid state. These compounds have in common that in addition to the covalently bonded alkoxy or aryloxy group, two... 

Alkoxides and aryloxides demonstrate similar chemistry to that of hydroxides in that it is possible to prepare mixed metal or double metal derivatives similar to hydroxo salts such as Na2[Sn(OH)6]. The formation of mixed metal alkoxides, e.g. Na2[Zr(OEt)6] and Ln[Al(OPri)4]3, is typically a result of the electron deficiency (Lewis acidity) of the metal centers in units of the type M(OR)x or M(OAr)JC (x < 5). This then leads either to oligomerization via alkoxide bridges or, in the presence of other alkoxides, to the formation of mixed metal compounds. 

PHYSICAL AND SPECTROSCOPIC PROPERTIES OF METAL ALKOXIDES AND ARYLOXIDES, M(OR),... 

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