Cr-bond metathesis reaction

Scheme 13 Generalized mechanism for the alkene insertion and cr-bond metathesis reactions catalyzed by lanthanocenes...

On the other hand, the reaction of CpfLnR with propylene did not afford any polymers but rather an allyl complex, Cp Ln(f/3-allyl), via a cr-bond metathesis reaction [56,117]. One molecule of propylene can insert itself into the Lu-Me bond of CpfLuMe to give the corresponding isobutylene complex. The successive insertion of propylene is 1000-fold slower than the first insertion [57]. The gas-phase reaction of Sc(CH3)2 with propylene also produces a... 

Essential to the cr-bond-metathesis reaction is donation of M—R bond density into the H—H antibonding orbital. As a consequence, lower barriers should result... 

Interestingly, the complexes CpCp Hf(SiHPhSiHPhSiH2Ph)Cl and CpCp Hf(SiHPh SiH2Ph)Cl are observed to form concurrently with the small polysilanes. It seems that these complexes are not necessarily the intermediates in the dehydrogenative process as suggested in Scheme 6, but perhaps only side products formed via non-productive cr-bond metathesis reactions (equation ll)22. 

Figure 4.26. Energy profiles for cr-bond metathesis reactions in kcal/mol.

In this chapter, we have summarized work from a number of laboratories that demonstrates that PHIP is a useful tool for the study of mechanistic organometallic chemistry. While the enhanced signals of PHIP provide nominally simple evidence for pairwise addition of H2, PHIP can be employed in many cases to determine much more complicated aspects of reaction mechanisms involving hydrogen addition. It is important to note, however, that PHIP has yet to be observed in cr-bond metathesis reactions or in metal-dihydrogen complexes. 

Isotopic labeling of alkane substrates for the investigation of EIEs in intermolecular exchange reactions such as oxidative addition reactions, cr-bond metathesis reactions, and 1,2-addition reactions has also been explored by various... 

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