Phosphorus hydride precursors

NMR measurements of 1H, 13C, and 31P may be very informative about the structure of the complex. The hydride precursor of the catalyst has a trigonal bipyramidal structure in which the two phosphorus ligands present can occupy either two equatorial sites or one axial and one equatorial site (Fig. 6.6). 

To be useful as CVD precursors, a metallo-organic compound should be stable at room temperature so that its storage and transfer are not a problem. It should also decompose readily at low temperature, i.e., below 500°C. The compounds listed in Table 4.1 meet these conditions with the exception of the alkyls of arsenic and phosphorus, which decompose at higher temperatures. For that reason, the hydrides of arsenic and phosphorus are often preferred as CVD precursors (see Ch. 3). These hydrides however are extremely toxic and environmental considerations may restrict their use. 

An expeditious and highly diastereoselective synthesis of (Z)-2-alkylsulfenyl (or 2-cyano) -2,4-diarylthietanes 53 has been reported by nucleophile (CN, RS") induced cyclization of the corresponding O,O-diethyl 5-(l,3-diaryl-3-oxopropyl) phosphorodithionates under microwave irradiation in solvent free conditions <02S1502>. This reductive cyclization can be considered to be induced by the attack of a hydride ion on the carbonyl carbon of the Michael adduct precursor to give an alkoxide ion, which attacks the phosphorus atom intramolecularly. 

Water-free AICI3 acts as a strong Lewis acid in the organic chemistry, especially in Friedel-Crafts-reactions for the alcylation of aromatics, e.g. in the production of ethyl benzene. It is a catalyst for the production of ethyl chloride and is a precursor material for the production of dyes, detergents, resins, aluminum borohydride, lithium aluminum hydride, and of phosphorus and sulfur compounds. 

Compound (27), formed at -78°C by hydride addition at the corresponding cationic carbonyl precursor, converts to the hydride (28), which contains 7 -diphosphine, above -50°C. It is believed that this conversion is fast enough to account for the exchange of phosphorus atoms in the hydride with AG297K = 18 kcal moP " It is a pity that the mechanistic details of many such interchanges are more speculative than experimentally established, since the study of intramolecular reactions of this sort provides access in principle to the mechanisms of important intermolecular reactions. 

An efficient diastereo- and enantio-selective reductive coupling of alkenylazaarenes with ketones has been developed, which provides aromatic heterocycles bearing tertiary-alcohol-containing side chains, with copper(II) acetate and Taniaphos SL-TOOl-1 as the catalytic system and phenylsilane is the hydride source." Mixed phosphorus-sulfiir ligands derived from carbohydrates are good catalyst precursors... 

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