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The use of sodium in alumina and silica gels for the reductive cleavage of the N–O bond of N-methoxy-N-methylamides, commonly referred to as Weinreb amides, has been investigated. This method reduces a diverse set of Weinreb amides with different functional groups to give modest to excellent yields. In the course of the studies to explore mechanisms and functional group tolerance, an apparently novel group transfer emerged, implying base-promoted cleavage of the Weinreb amide to form formaldehyde, followed by aldol condensation.

A few decades ago the phrase organic materials brought to mind only insulating polymers. Organic metals and organic superconductors have dramatically changed that perception and opened the materials science field to the full range of molecular architecture manipulation that is the forte of organic chemists. In a similar vein, the term salts generally con­ veyed a picture of insulating inorganic crystals with simple cations and anions, although many organic ions were known. With the synthesis by Pedersen, Lehn, Cram, and others of large organic complexants for metal cations, new classes of salts with thousands of different complex ions became available ( 1-7). When a suitable non-reducible organic complexant, L, is combined with an alkali metal, M, the formation of the complexed alkali cation, M+L, releases an electron. This electron can either combine with an alkali metal to form the alkali metal anion, M-, or become trapped in the solvent or in the ionic lattice to form the solvated electron, or a crystalline electride, respectively. Crystalline electrides sometimes behave as saits, in which the electrons are localized in the vicinity of the anionic sites, and sometimes as expanded metals (or near metals), in which the electrons are itinerant. This review focuses on the optical, magnetic, and electronic properties of these unusual new compounds (8, 8a-f).

Transition-metal nitrides have been synthesized by heating nanoscale metal particles under flowing N2(g) or NH3(g). In some cases reaction temperatures are significantly lower than those required by conventional heating procedures. Nanoscale metal particles of Mo, Nb, Ta, Fe−Mo, Fe−Nb, and Cu−Nb were prepared by reduction of the respective metal chloride or mixture of chlorides with the sodide, [K+(15-crown-5)2]Na-, in dimethyl ether solution. The previously characterized nitrides that were prepared (with synthesis conditions indicated) include γ-Mo2N (800 °C, N2) and Mo2N (720 °C, N2), Ta3N5 (650 °C, NH3), Fe3Mo3N (>650 °C, N2), and a mixture of niobium nitride phases (800 °C, N2). A previously unreported phase has been found in the Ba−Nb−N system.

Electron transfer from an alkali metal to a suitable complexant for the cation can yield crystalline ionic solids that contain the complexed cation and either an alkali metal anion (alkalide) or a trapped electron (electride). The nature and properties of electrides are emphasized in this paper. When the organic complexant contains aromatic groups, the anionic species is an aromatic radical anion. Preliminary work on the addition of alkali metals to LOGEAs (large organic globular electron acceptors) is described and strategies for the synthesis of mixed electride-anion compounds are considered.

Electrides are materials in which alkali metals (Li through Cs) ionize to form bound alkali cations and “excess” electrons. The electrons reside in large cavities or channels or both in the host lattice. We report here the first synthesis of thermally stable inorganic electrides with cation-to-electron ratios of 1:1 as in organic electrides. Although alkali metal adducts to alumino-silicate zeolites are well known, the cation-to-electron ratio is generally 3:1 or greater because these zeolites contain alkali cations prior to incorporation of the alkali metal. In this work, two pure silica zeolites, ITQ-4and ITQ-7, with pore diameters of ∼7 A, absorb up to 40 wt % cesium from the vapor phase (even at room temperature). The other alkali metals (except Li) can also be introduced at elevated temperatures. The optical and magnetic properties of the cesium-loaded samples suggest ionization to form Cs+ and e- with substantial electron-spin pairing. The metal-loaded samples are stable to at least 100 °C and are a...

Electrides are ionic solids with cavity-trapped electrons, which serve as the anions. Localization of electrons in well-defined trapping sites and their mutual interactions provide early examples of quantum confinement, a subject of intense current interest. We synthesized the first crystalline electride, Cs(+)(18-crown-6)(2)e(-), in 1983 and determined its structure in 1986; seven others have been made since. This Account describes progress in the synthesis of both organic and inorganic electrides and points to their promise as new electronic materials. Combined studies of solvated electrons in alkali metal solutions and the complexation of alkali cations by crown ethers and cryptands made electride synthesis possible. After our synthesis of crystalline alkalides, in which alkali metal anions and encapsulated alkali cations are present, we managed to grow crystalline electrides from solutions that contained complexed alkali cations and solvated electrons. Electride research is complicated by thermal instability. Above approximately -30 degrees C, trapped electrons react with the ether groups of crown ethers and cryptands. Aza-cryptands replace ether oxygens with less reactive tertiary amine groups, and using those compounds, we recently synthesized the first room-temperature-stable organic electride. The magnetic and electronic properties of electrides depend on the geometry of the trapping sites and the size of the open channels that connect them. Two extremes are Cs(+)(15-crown-5)(2)e(-) with nearly isolated trapped electrons and K(+)(cryptand 2.2.2)e(-), in which spin-pairing of electrons in adjacent cavities predominates below 400 K. These two electrides also differ in their electrical conductivity by nearly 10 orders of magnitude. The pronounced effect of defects on conductivity and on thermonic electron emission suggests that holes as well as electrons play important roles. Now that thermally stable organic electrides can be made, it should be possible to control the electron-hole ratio by incorporation of neutral complexant molecules. We expect that in further syntheses researchers will elaborate the parent aza-cryptands to produce new organic electrides. The promise of electrides as new electronic materials with low work functions led us and others to search for inorganic electrides. The body of extensive research studies of alkali metal inclusion in the pores of alumino-silicate zeolites provided the background for our studies of pure silica zeolites as hosts for M(+) and e(-) and our later use of nanoporous silica gel as a carrier of high concentrations of alkali metals. Both systems have some of the characteristics of inorganic electrides, but the electrons and cations share the same space. In 2003, researchers at the Tokyo Institute of Technology synthesized an inorganic electride that has separated electrons and countercations. This thermally stable electride has a number of potentially useful properties, such as air-stability, low work function, and metallic conductivity. Now that both organic and inorganic electrides have been synthesized, we expect that experimental and theoretical research on this interesting class of materials will accelerate.

Alkali metals in silica gel (the Na2K-SG(I) reagent) cleanly effect Birch reductions of substrates with at least two or more aromatic rings. The reaction conditions are alcohol-free, ammonia-free, and achieve excellent yields and high selectivities at room temperature.

Alkali metals in silica gel (the M-SG materials) are effective reagents for reductive deallylation, debenzylation, debenzhydrylation, and detritylation of amines. As such, these reagents provide a convenient alternative to traditional metal ammonia solutions for this class of deprotections.

Alkali metals absorbed in silica gel (the M-SG reagents) efficiently cleave C-P bonds in triaryl- and diarylphosphines. The resulting alkali metal phosphides can serve as useful building blocks for a variety of phosphines. Alkyldiarylphosphines undergo exclusive aryl group cleavage.

A novel method for the desulfonation of secondary amines is described. Alkali metals absorbed into nanostructured silica (M-SG) were found to be useful solid-state reagents for the desulfonation of a range of N,N-disubstituted sulfonamides. M-SG reagents are room-temperature-stable free-flowing powders that retain the chemical reactivity of the parent metal, decreasing the danger and associated cost of using reactive metals.

Alkali metals absorbed into silica gel yield three stages of unique loose black powders (M-SG) that are strong reducing agents. All react nearly quantitatively with water to form hydrogen. Liquid Na-K alloys form air-sensitive powders at room temperature that can be converted at 150 degrees C to a form that is sensitive to moisture but not to dry air. Slowly heating sodium and silica gel to 400 degrees C yields a third type that can be handled in ambient air with only slow degradation by atmospheric moisture. These materials eliminate many hazards associated with pure alkali metals and provide easily handled reducing agents and hydrogen sources. They could be used in continuous-flow reactors to reduce and protonate aromatics, dechlorinate alkyl and aryl halides, and desulfurize various compounds.

The isostructural sodides (I) (space group P212121) are synthesized in a "K-cell" by using previously reported techniques (no details given).

The crystal structures of Rb + (15-crown-5) 2 Na - (I) (monoclinic, space group C2/m, a=11.555 (3) A, b=13.587 (3) A, c=9.958 (3) A, β=92.03 (2)˚, V=1562.4 (7), A 3 , Z=2) and Cs + (18-crown-6) 2 Na - (II) (monoclinic, space group C2/c, a=13.581 (3) A, b=15.684 (2) A, c=17.429 (4) A, β=93.16 (2)˚, V=3706.8 (15) A 3 , Z=4) have been determined by single-crystal X-ray diffraction. The agreement factors are R=0.044 and R w =0.052 for I and R=0.028 and R w =0.033 for II