Transition metal hydride complexes, reactions

The analogous reactions of Zn and Cd derivatives arc less well studied. Zinc alkyls ZnRi (R = Et, n-Bu) react with transition-metal hydride complexes, H2M(Cp-(M = Mo, W) ... 

Many more examples have been collected for the reaction of transition metal hydride complexes with 1,3-dienes, which appear to proceed via radical pair mechanisms, even without photochemical activation72-77. The following general mechanism has been assumed to be operative for the reaction of HMn(CO)572,73, HFe(CO)4SiCl374,75, HFe(CO)2Cp76 and HCo(CO)4 (H-[M]) (equation 18)77. 

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... 

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. 

S.8.3.2.2. by Reaction with a Transition or Inner Transition-Metal Hydride Complex. 

S.4.2. by Reaction of an Organotin Azide with a Transition- or inner Transition-Metal-Hydride Complex. 

SCF and CAS SCF calculations on mono and bimetallic transition metal hydride complexes are reported. The importance of including the non dynamical correlation elTects for the study of the cis-trans isomerism in dihydrido complexes and for the study of the CO insertion reaction into the metal hydride bond is stressed. The metal to metal hydrogen transfer in a class of bimetallic d — d hydride complexes is analyzed and the feasibility of the transfer discussed as a function of the coordination pattern around the two metal centers. 

The ability to catalyze certain reactions of molecular hydrogen homogeneously in solution has been demonstrated for many transition metal ions and complexes (34)—among them complexes of Cu Cu Ag Hg Hgi, Col, Coll, pdii, Ptii, Rhi, Rh i, Ru i Ruiii, and Ir. In each case it appears that H2 is split by the catalyst with the formation of a reactive transition metal hydride complex (which may or may not be detected) as an intermediate. Three distinct mechanisms by which this can occur have been recognized (34), which are exemplified by the following reactions. 

The ease of reversal of alkene insertion is evident from the numerous syntheses of transition metal-hydride complexes using main group metal alkyls as the source of hydride. The hydride in the products of such reactions usually arises from -hydride abstraction or elimination from intermediate unstable transition metal alkyls. This idea is reinforced by the greater effectiveness of secondary alkyls such as isopropyl or cyclohexyl compounds. However, it has been shown that in at least one case the hydride results from hydrolysis of a Pt-Mg bond, not from the alkyl formed from reaction of a Pt-Cl bond with a Grignard reagent. Several of the reactions listed in Table 1 are spontaneously reversible. Reactions where -hydride elimination has been used in the synthesis of hydrides are listed in Table... 

Insertion Reactions of Acetyienes 11.2.3.2. Transition Metal Hydride Complexes... 

There are only limited pKj, scales for transition metal hydride complexes compared to the extensive scales for organic and inorganic acids, despite the fact that hydrides often mediate organometallic reactions these were reviewed in 1991 [42]. Most of these complexes contain carbonyl and/or phosphine ligands and are usually insoluble in water. The for about 20 neutral hydrido-carbonyl... 

Transition metal hydride complexes are important starting materials for reactions with [Au(PPh3)]". The foundation for this method is the isolobal relationship between [AulPPhj)] and Although many examples... 

The transition metal hydride complexes thus produced can react further with various unsaturated compounds such as alkenes and alkynes to undergo insertion reactions giving transition metal alkyl and alkenyl compounds. 

The M-H bonds of transition-metal hydride complexes may be cleaved heterolyti-cally (H, H transfer) or homolytically (H transfer). AG for the transfer in Equation 1.1 is readily quantified by pKj measurements (see Chapter 3). Analogous measurements for H transfer, or hydricities , are difficult because the loss of generates a vacant coordination site. However, AG for Equation 1.2 can be determined indirectly, from electrochemical and pJG measurements in the appropriate solvent [1, 2], and we can thus compare the hydricities of various hydride complexes (see Chapter 3). The lowest values of AG. (corresponding to the complexes most eager to transfer H ) are found for second- and third-row transition metals [3], which is why those (relatively expensive) metals are good donors and effective catalysts for reactions like ionic hydrogenation [5-10],... 

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