High-energy ball milling has been successfully employed to produce alkaline earth carbides from the elements. In particular, CaC(2) yields of up to 98% can be realized in as little as 12 h. Similarly, the carbides of Mg (39% yield), Sr (87% yield), and Ba (82% yield) have been prepared. An intermediate in the synthesis of CaC(2) is the newly discovered gold-colored Ca-graphite intercalation compound CaC(6). Sr and Ba also go through initial intercalation phases (SrC(6) and BaC(6)) before ultimately producing the carbides. The magnesium product consisted of Mg(2)C(3) with no MgC(2) observed. The addition of sulfur to CaC(2) forming reactions did not adversely affect the overall synthesis; this suggests that this method may be utilized to sequester sulfur from high-sulfur coal. The preparation of these compounds by high-energy ball milling represents a novel method for producing pure carbides, as well as a convenient route to isotopically enriched ethyne.
This paper describes
the synthesis and characterization of RP(o-biphenyl)2 phosphine ligands (where R = PhO,
Ph, and t-Bu), corresponding gold(I) chloride precatalysts,
gold(I) triflate catalysts, and gold(I) π-complexes. All ligands
and gold chlorides and three π-complexes were characterized
in the solid state. The most significant differences between complexes
in the solid state were varying P–Au bond lengths, a consistent
reflection of the different electronic character of each phosphine.
NMR spectroscopic data on enol ether π-complexes is consistent
with increasing cationic character in the alkene fragment, from R
= t-Bu to R = Ph and OPh. The intermolecular alkene
exchange process for [LAu(methoxypropene)]SbF6 (L = PhO(o-biphenyl)2P) is faster than that of the analogous
complex with t-Bu2(o-biphenyl)P,
presumably due to the higher electrophilicity of the former complex.
Examination of a series of vinyl silane π-complexes with triaryl
phosphine ligands reveals increasing stability and ease of preparation
(Ph3P < Ph2P(o-biphenyl)
< PhP(o-biphenyl)2). These results
reveal that incorporation of a second biphenyl substituent into ligand
architectures allows preparation of a series of gold π-complexes
with increased stability over a range of phosphine donicity.
Mechanochemical metathesis reactions were utilized to synthesize nanocrystalline ZrSi(2) ranging from 9-30 nm in size. Size was controlled through dilution with CaCl(2). A linear relationship was found between diluent concentration and crystallite size. Unlike typical self-propagating metathesis reactions, this reaction did not self-propagate, requiring the input of mechanical energy.
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