Ruthenium polyhydrides

Ruthenium polyhydride complexes containing monophos-phaferrocenes are now available. In contrast to Cp ruthenium chemistry, the use of a trispyrazolyborate ligand favors the formation of dihydrogen structures the chemistry of Tp... 

A convenient route to a synthetically useful ruthenium polyhydride complex is the reaetion of Ru (COD) (COT) with 2 equiv. of tricyclohexylphosphine under hydrogen ... 

Ruthenium polyhydrides also activate C-H bonds e.g., H-D exchange can occur in arenes using an RUH4P3 complex where the P ligands are sterically demanding. This presumably involved intermediates resulting from oxidative addition of an arene C-H bond d. 

A review by Darensbourg and Ash on anionic transition metal-hydrides has appeared during the reporting period. So has a review of ruthenium species by Halpern which devotes much attention to ruthenium polyhydrides. Both reviewers emphasize hydrogenation catalysis. 

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. 

Mo(r75-C5H5)2H2] and [MoH dppe ]. Our studies of the di- and trihydride complexes of ruthenium and iridium, described above and published previously (27,35), and those of other workers (discussed at the beginning of this chapter), indicate that photoinduced elimination of molecular hydrogen is a common reaction pathway for di- and polyhydride complexes. To demonstrate the photoreaction s generality and its utility for generating otherwise unattainable, extremely reactive metal complexes, we have begun to study the photochemistry of polyhydride complexes of the early transition metals. We focused initially... 

Hydrogen bonding is a well-known phenomenon that has led to major developments during the last decade in the field of polyhydrides. The formation of the so-called dihydrogen bond (M H- H X) can occur intermolecularly between a hydride and a weak acid (see equation 4) or intramolecularly between a hydride and a pendant ligand with an NH or OH group. This type of interaction is very important as it may control reactivity and selectivity in solution. A few examples have appeared in ruthenium chemistry. 28... 

After the advent of the nonclassical if-Vi.2 complexes, polyhydrides had to be reinterpreted [14]. Thus, RuH4(PPh3)3 is not a classical tetrahydride of coordination number seven at the ruthenium atom but a dihydride-dihydrogen complex Ru(H2)(H)2(PPh3)3 of octahedral geometry [25]. 

A number of ruthenium complexes react directly with dihydrogen to produce polyhydrides "". ... 

The scope of the review is limited to ruthenium- and osmium- triisopro-pylphosphine polyhydrides. Under the point of view of Scheme 1, many more polyhydride systems have not been studied. If one takes into account that there are certain properties characteristic for each metal, the development of new types of coupling reactions and the formation of novel ligands should be observed in the near future, by using polyhydrides of metals different from ruthenium and osmium. 

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