Hydrogen metal hydride complexes

In 1931, Hieber and Leutert reported Fe(CO)4(H)2 not only as the first iron hydride complex but also as the first transition-metal hydride complex (FeH2 was reported in 1929 from FeCl2 and PhMgBr under a hydrogen atmosphere. However, it exists only in a gas phase) [2, 3]. The complex synthesized from Fe(CO)5 and OH (Scheme 1) is isolable only at low temperature and decomposes at room temperature into Fe(CO)5, Fe(CO)3, and H2. 

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)]. 

Mdssbauer spectra of bonding and structure in, 15 184-187 reactions with diborane, 16 213 stabilization of, 5 17, 18-19 cyanates, 17 297, 298 cyanide complexes of, 8 143-144 cyclometallated bipyridine complex, 30 76 diazene complexes, 27 231-232 dinitrogen complexes, 27 215, 217 diphosphine complexes of, 14 208-219 dithiocarbamates, 23 253-254 -1,2-dithiolene complexes, 22 323-327 hydrogen bonding, 22 327 halide complexes with phosphine, etc., 6 25 hexaflouride, structure, 27 104 hydride complexes, 20 235, 248-281, see also Transition metal-hydride complexes... 

A variety of factors contribute to the great current interest in l polynuclear metal hydride complexes. These include the novel geometries found in these systems and their usefulness as models for the bonding of hydrogen to metals, such as may occur in catalysis (i) or hydrogen-storage applications (2). A comprehensive review of metal hydride complexes, in which polynuclear species are included, has been published by Kaesz and Saillant (3). 

The photochemical studies of transition metal hydride complexes that have appeared in the chemical literature are reviewed, with primary emphasis on studies of iridium and ruthenium that were conducted by our research group. The photochemistry of the molybdenum hydride complexes Mo(tj5-C5H5)2M2] and [MoH4(dppe)2] (dppe = Ph2PCH2CH2PPh2), which eliminate H2 upon photolysis, is discussed in detail. The photoinduced elimination of molecular hydrogen from di-and polyhydride complexes of the transition elements is proposed to be a general reaction pathway. 

For a more complete description of the principles of transition metal catalysis, a number of the excellent reviews published recently should be consulted. These include, in addition to those already cited, several reviews of rhodium (89) and palladium (90-93) chemistry, addition (94, 95) and insertion (96) reactions, homogeneous catalytic hydrogenation (97), hydride complex chemistry (98), nitrogen fixation (99), and organometallic complexes as potential synthetic reagents (100). 

L. Vaska and J. W. DiLuzio, On the origin of hydrogen in metal hydride complexes formed by reaction with alcohols, J. Am. Chem. Soc., 8 (1962) 4989 1990. 

Phase B nearly always requires the dissociation of a ligand from ihc coordination sphere of the metal hydride complex formed in situ to produce a vacant coordination site, followed by coordination and insertion of the hydrocarbon into the reactive metal- hydrogen bond, as in following example an K... 

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