Hydrides synthesis from molecular hydrogen

However, since the goal of this work was the synthesis of alcohols from olefins via hydrohydroxymethylation (75, 76), little attention was given to developing a shift-catalyst per se. Pettit has recently reexamined some of this work and shown that, by careful control of the pH of the reaction mixture, systems based on either Fe(CO)5 or Cr(CO)6 can be developed for the production of either formic acid or methanol from carbon monoxide and water (77, 78). Each of these latter systems involves the formation of metal hydride complexes consequently, molecular hydrogen is also produced according to the shift reaction [Eq. (16)]. 

The universality of molecular hydrogen complexes has extended to dinuclear complexes [5b], bioinorganic compounds [11], and rare earth metals [6]. Apart from leading to synthesis of new compounds, the study of molecular hydrogen complexes has revived interest on compounds considered classically as polyhydrides. Many of these compounds have been reformulated to contain the dihydrogen ligand, with more reasonable coordination numbers and oxidation states than those predicted for polyhydrides. For instance, the [Fe(PR3)3H4 complex that was considered to be a heptacoordinated Fe(IV) polyhydride [12] has recently been understood to contain a H2 ligand and two hydrides with a much more common octahedral d ML structure, and an oxidation state of (II) for the iron [4a]. 

The reaction mechanism of photocyclization of aryl vinyl ethers was derived from results obtained by means of flash photolysis. The ground state intermediate rearranges by mono-or bi-molecular 1,4-hydrogen shifts to yield the products (Scheme 62) (81JOC978). The photocyclization of 2-aryloxyenones was used in the total synthesis of ( )-lycoramine (77JA8065). The formation of dihydrobenzo[6 ]furans by radical cyclization from o-allenyl-oxyarenediazonium salts with tri-n-butyltin(IV) hydride was successful (81CC136). 

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