Hydride complexes reactivity

The chemistry of [Rh(OEP)h in benzene is dominated by Rh—Rh bond homolysis to give the reactive Rh(Il) radical Rh(OEP)-. This contrasts with the reactivity of fRh(OEP)] in pyridine, which promotes disproportionation via the formation of the thermodynamically favorable Rh(IlI). ct complex [RhjOEPKpy) ] together with the Rh(l) anion, Rh(OEP)J The hydride complex Rh(OEP)H shows NMR chemical shift changes in pyridine consistent with coordination of pyridine, forming Rh(OEP)H(py). Overall, solutions of Rh(OEP)l in pyridine behave as an equimolar mixture of [Rh(OEP)(py ) and (Rh(OEP). For example, reaction... 

Table 10 shows the results of polymerization of oc-olefins catalyzed with trivalent complexes. When a bulkiler tBuMe2Si group instead of the Me3Si group was introduced into the yttrium complex, the racemic complex was formed exclusively [74c]. However, this alkyl complex did not react with olefins, and hence it was converted to a hydride complex by reaction with H2. The complex obtained was reactive to various olefins and produced polymers at... 

Palladium(O) forms a complex with quinone that is now electron rich and can be protonated to give hydroquinone and palladium(II). The latter can start a new cycle via a carbomethoxy species after reaction with methanol and CO (c.f. reaction (6), Figure 12.4). Thus we have formally switched from a hydride initiator to a carbomethoxy initiator species. Addition of quinone to a nonactive or moderately active palladium system is a diagnostic tool that tells us whether zerovalent palladium is involved as an inactive state. Likewise, one might add dihydrogen to a system to see whether palladium(II) salts need to be converted to a hydride to reactivate our dormant catalyst. 

The mechanism of the catalytic cycle is outlined in Scheme 1.37 [11]. It involves the formation of a reactive 16-electron tricarbonyliron species by coordination of allyl alcohol to pentacarbonyliron and sequential loss of two carbon monoxide ligands. Oxidative addition to a Jt-allyl hydride complex with iron in the oxidation state +2, followed by reductive elimination, affords an alkene-tricarbonyliron complex. As a result of the [1, 3]-hydride shift the allyl alcohol has been converted to an enol, which is released and the catalytically active tricarbonyliron species is regenerated. This example demonstrates that oxidation and reduction steps can be merged to a one-pot procedure by transferring them into oxidative addition and reductive elimination using the transition metal as a reversible switch. Recently, this reaction has been integrated into a tandem isomerization-aldolization reaction which was applied to the synthesis of indanones and indenones [81] and for the transformation of vinylic furanoses into cydopentenones [82]. 

Bursten, B. E. and Gatter, M. G. (1984). Molecular orbital studies of organometallic hydride complexes 2. The correlation of hydrogen atom reactivity with valence orbital energetics. Organometallics 3, 895. 

In view of the chemical reactivity of the tertiary phosphine and nickel hydride complexes to air, all manipulations should be carried out in a nitrogen or argon atmosphere.6 All solvents should be distilled under a nitrogen or argon atmosphere. 

The reactivity of the samarium hydride complex is evidenced [170] by the formation of [Cp2Sm(THF)]2[/4-72-(OSiMe20SiMe20)] a bridged samarium siloxide, from [Cp2Sm(/r-H)]2. The samarium hydride complex is also used in the polymerization of methyl methacrylate [171]. 

---