Preparative metal-rich halides

Many reduced (metal-rich) halides of group 4 (especially Zr) and the rare earth metals have been prepared. Most of these compounds are stabilized, by the metals forming Mg octahedral or other clusters having strong metal-metal bonds. The reactions to form these clusters are slow. Other nonmetals, especially oxygen, are undesirable impurities that may form more stable phases. Therefore the reactions are carried out with stoichiometric mixtures of pure halide and metal in degassed Ta or Nb tubes that have been loaded in an inert atmosphere and arc-welded shut. The welded ampule is then sealed in a protective quartz tube and heated to a temperature adequate to achieve a reaction in a week or more ( >600°C) . Yields may be small in some cases individual single crystals are produced as evidence of synthesis of a new material with metal-metal bonds. 

Controlled preparation of compounds has to precede any measurement of their physical properties (Schafer 1971). In particular, this remark holds for the research on metal-rich halides of rare earth elements which is marked by trial and error in the early stages. Often, phases could only be prepared as a minority in multicomponent... 

Typically, Be-containing alloys and intermetallic phases have been prepared in beryllia or alumina crucibles Mg-containing products have been synthesized in graphite, magnesia or alumina crucibles. Alloys and compounds containing Ca, Sr and Ba have been synthesized in alumina , boron nitride, zircon, molybdenum, iron , or steel crucibles. Both zircon and molybdenum are satisfactory only for alloys with low group-IIA metal content and are replaced by boron nitride and iron, respectively, for group-IIA metal-rich systems . Crucibles are sealed in silica, quartz, iron or steel vessels, usually under either vacuum or purified inert cover gas in a few cases, the samples were melted under a halide flux . 

In the reaction of group 13 element halides with metal carbonyl dianions, the analysis is more complex than observed for the reactions with metal monoanions. Upon addition of metal dianions to EX3 or REX3, either one or two halide ions may be eliminated. When only one halide ion is eliminated per added metal dianion, the complexes may still be viewed as E3+ derivatives (Equations (33)-(36)).19 This may be controlled to some extent by the stoichiometry of the reaction. Comparison of Equations (33)19 and (34)19 shows that the electron demand at the main group element can be satisfied by coordination either to an electron-rich metal center 26 or formation of a halide bridge 27. Ligand-stabilized forms may also be prepared in this fashion (Equation (36)).19... 

Apart from their behaviour as ligands in metal catalyst systems, studies of the reactivity of phosphites towards a wide variety of other substrates have attracted attention. New aspects and applications of the classical Michaelis-Arbuzov reaction and its variants continue to appear. Evidence of the thermal disproportionation of methyltriaryloxyphosphonium halides formed in the reactions of triarylphosphites with alkyl halides, together with the formation of P-O-P intermediates, has been reported. The Michaelis-Arbuzov reaction has been used in the synthesis of phosphonate-based styrene-divinylbenzene resins and polyphosphonated chelation therapy ligands.Treatment of electron-rich benzylic alcohols dissolved in triethylphosphite with one equivalent of iodine affords a low-temperature one-pot route to the related benzylic phosphonates, compounds which are otherwise difficult to prepare. Upper-rim chloromethylated thiacalix[4]arenes have also been shown to undergo phosphonation on treatment with a phosphite ester in chloroform at room temperature. The nickel(II)-catalysed reaction of aryl halides with phosphite esters in high boiling solvents, e.g., diphenyl ether, (the Tavs reaction), has also... 

Heterobimetallic complexes have recently attracted considerable attention in light of the promise of enhanced reactivity as a result of the cooperativity between adjacent, but electronically different, metal centers. A large number of these bimetallic compounds have been synthesized by the reactions of organometallic halides with anionic metal carbonyls. Here, we describe an extension of this route to the synthesis of hydride rich. Os—Zr and Os—Rh complexes by the reaction of organometallic halides with a metal poly hydride anion. These preparations demonstrate the synthetic utility of transition metal polyhydride anions. 

Heteroarylzinc compounds are of particular use in palladium-catalysed couplings, being compatible with many functional groups. They have usually been prepared by exchange reactions (in situ) of zinc halides with heteroaryllithi-ums but this method limits their usefulness. Efficient methods are now available for their direct preparation from zinc metal and the heteroaryl halide in both electron-rich and electron-poor systems. 

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