Hydrogen Transfer to the Metal

Formation of Bonds between Hydrogen and Transition Metals 227 1.10.8 by Hydrogen Transfer to the Metal 1.10.8.1. from Alcohols in Basic Media. 

Conversion of a metallocarboxylic acid to a hydride complex is supposed to occur via a hydrogen transfer to the metal as CO2 is eliminated ... 

Figure 18. DFT optimized structure of the transition states for unimolecular /3-hydrogen transfer to the metal, on the left, and bimolecular /3-hydrogen transfer to the monomer, on the right. " ...

Allylic activation represents a possible evolution path for the intermediate which is obtained after unimolecular /3-hydrogen transfer to the metal, that is, the olefinic chain end coordinated to the metallocene hydride complex. The DPT calculations of Ziegler and co-workers on the geometrically costrained H2Si(Cp)(NH)Ti-R+ system and of Brintz-inger and Prosenc on the Cp2Zr(methallyl)+ system ... 

It is worth noting that, when /3-transfer events are not negligible with respect to propagation, the slower state could correspond to initiation centers deriving from some kind of chain release that does not involve the monomer (e.g., a /3-hydrogen transfer to the metal rather than to a coordinated monomer molecule). The occurrence of a nonlinear propagation rate law is discussed in ref 509. 

P(OMe)3] with Ati=4.2x 10 s" (30 °C). As with the osmium complexes just discussed this rate is several orders of magnitude lower than that of methane elimination from the corresponding methyl hydride while reductive elimination of methane from [Co(Me)2 P(OMe)s 4]+ exhibits an intermediate reactivity. The latter reaction is consequently thought to proceed via a multistage mechanism in which carbene complexes (resulting from a-hydrogen transfer to the metal) play an important role. Elimination of CH4 from the methyl hydride complex is probably a concerted process according to these workers. 

---