Iron dihydrogen complex

Another example of selective C=C bond hydrogenation has arisen from mechanistic studies on an iron m-hydride dihydrogen complex, [Fe(PP3)(FI)(H2)](BF4) [PP3 = P(CH2CH2PPh2)3], a catalyst inactive with alkene substrates. Scheme 6 shows that no decoordination of dihydrogen is required in any step of the cycle and that the vacant site is created by unfastening of one of the P-donor atoms (species (16)).50 Extensive studies on catalytic alkene hydrogenation by analogous tripodal (polyphosphine) Rh, Os, and Ir complexes have been carried by Bianchini and co-workers.51,52... 

Greg Kubas of Los Alamos National Laboratory has determined how hydrogen interacts with metals. The important part of his work is that hydrogen, a substrate that is redox inactive substrate and not Brpnsted acidic, transforms upon complexation whereupon the coordinated H2 becomes acidic. The deprotonation of a metal dihydrogen complex generates oxidizable species and in this way, H2 is connected to electrons and heterolytic activation. Rauchfuss explained that Kubas discovery has helped guide his team s effort to connect H2 binding to this redox-active iron metal. 

Field has found that the iron dihydride complex Fe(dmpe)2H2 (dmpe= Me2PCH2CH2PMe2) can be irradiated at low temperature to induce loss of dihydrogen. The Fe° fragment formed then reacts with pentane to give the n-pentyl hydride oxidative addition product [94]. Irradiation in liquid xenon containing... 

Hundreds of iron hydride complexes with phosphine ligands have been isolated and characterized. These complexes are almost always diamagnetic. For example, a spectacularly active electrocatalyst for dihydrogen oxidation is the cyclopentadienyl iron... 

Jia has observed that protonation at room temperature of the iron hydride in eq 34 results in a spectroscopically observable dihydrogen complex (5 -12.5, Tj (min) = 5 ms, and = 30.7 Hz) prior to thermal loss of H2 and decomposition [34]. In contrast to the Cp ligand used by Lapinte (eq 13) [32] which donates electron density into the a of the dihydrogen complex to favour dihydride complex formation, the electron poor Cp disfavours dihydride complex formation. 

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