Atom synthesis

Two Nitrogen Atoms and One Oxygen Atom Synthesis of 1,3,4-oxadiazines 98H(49)557. 

One of the m jor attractions in the metal-atom synthesis of dimer and cluster species is the ability to isolate highly unsaturated species, M Lm, that may then be considered to be models for chemisorption of the ligand, L, on either a bare, or a supported, metal surface (,100). It is quite informative to compare the spectral properties of these finite cluster-complexes to those of the corresponding, adsorbed surface-layers (100), in an effort to test localized-bonding aspects of chemisorption, and for deciphering UPS data and vibrational-energy-loss data for the chemisorbed state. At times, the similarities are quite striking. 

By 1977-78, the initial growth period of metal atom synthesis in organometallic chemistry was coming to an end. Various factors contributed to this slow-down. One was that a lot of the more... 

The general technique of the metal vapor experiments described below was to co-condense the vapors of the transition metal with those of the chosen hydrocarbon or hydrocarbon mixtures. In this paper we briefly outline the technique of metal atom synthesis and then show how it can be applied to alkane activation reactions. 

M. Matsumi, K. Naka, and Y. Chujo, Extension of ir-conjugation length via the vacant p-orbital of the boron atom. Synthesis of novel electron deficient ir-conjugated systems by hydroboration polymerization and their blue light emitting, J. Am. Chem. Soc., 120 5112-5113, 1998. 

Most metals vaporize as atoms, which are highly reactive as a result of the input of the heat of vaporization and the lack of steric restrictions. The basic strategy in metal atom synthesis is to codeposit the metal atoms with a large excess of reactant, thereby promoting reaction between the metal atom and the substrate and suppressing recombination to the bulk metal. As shown schematically in... 

Thermolysis on insulating wool. Kaowool or other refractory wools are valuable for reduced radiative heat losses from a hot crucible. However, their use causes some increase in the extent of pyrolysis of substrate vapor by the crucible assembly and this, in rare instances, may spoil a metal atom synthesis. Only one example is known at present. The reaction of palladium atoms with benzyl chloride gives very low yields of t73-benzylpalladium chloride when the palladium is evaporated from an alumina crucible insulated with Kaowool, but a 30-50% yield with an uninsulated crucible. It has been established that this is due to enhanced formation of product-destroying radicals on the hot Kaowool. 

As far as the chemist is concerned, nanosized materials are huge macromolecules (with molecular weights of the order of 106 to 1010) constructed from millions of atoms. Atom-by-atom synthesis of nanostructures, via covalent bond formation, is a formidable task which has not as yet been achieved by synthetic chemists. Covalent polymerization is the best that chemists have done thus far [3]. Chemists have made spectacular progress, however, in forming self-organized and supramolecular materials in the size domain of nanostructures by the non-covalent bond assembly of molecules [7]. 

All the methods used to evaporate metals for atom synthesis were developed originally for the deposition of thin metal films. The more important of these techniques are shown schematically in Fig. la-d. Most of the evaporation devices can be scaled to give amounts of metal ranging from a few milligrams per hour for spectroscopic studies to 1-50 gm/hour for preparative synthetic purposes. Evaporation of metals from heated crucibles, boats, or wires (Fig. la-c) generally gives metal atoms in their ground electronic state. Electronic excitation of atoms is possible when metals are vaporized from arcs, by electron bombardment, or with a laser beam (Fig. Id). The lifetime of the excited states of... 

Although the foregoing reactions are quite facile, they are not competitive with the very well-established conventional methods for synthesis of metallocenes. Cyclopentadiene, nevertheless, can be a useful substrate in metal atom synthesis as part of a mixed-ligand system (6, 110, 136, 140), e.g.,... 

---