Allyl group orbitals

FIGURE 21.13 The interaction of metal (/orbitals with the molecular orbitals on the allyl group. Note how the symmetry of the (/orbital on the metal matches that of the allyl orbital with which it interacts. 

Fio. 10. The molecular orbitals of the allyl group a (tli bonding), b nonbonding), and c 1/13 antibonding), and d, the metal d orbital overlap with ijif... 

In both schemes cis insertion is the most hypothetical step. Cossee has assumed 164) that similar processes take place during olefin polymerization in the presence of Ziegler-Natta catalysts, and in some other reactions catalyzed by the transition metal compounds. This author came to the conclusion 165) that the d orbitals of the metal combine with the migrating group to facilitate such processes. In the course of 7r-allyl transfer the palladium orbitals overlap with the antibonding orbitals of double bond of the <7-bonded allyl group so as to favor an insertion reaction. 

The allyl group most commonly functions as a trihapto ligand, using delocalized tt orbitals as described previously, or as a monohapto ligand, primarily ct bonded to a metal. Examples of these types of coordination are shown in Figure 13-24. 

The anodic oxidation of heteroatom compounds having a silyl group and a stannyl group on the same a-carbon has been examined [133]. The anodic oxidation in the presence of the allylsilane led to the selective cleavage of the C-Sn bond and the introduction of the allyl group on the carbon [Eq, (32)]. Probably the C-Sn a orbital interacts more... 

Next is the three-atom system, n-allyl, C3H5. In this case, there are three 2p orbitals to be considered, one from each of the carbon atoms participating in the n system. This situation can be viewed using the group orbital approach. The group orbitals here are derived from the parallel 2p orbitals on the terminal carbon atoms. 

Metals such as Li or Mg may move by way of the p3 allyl complex 22 from one end 21 to the other 23 of an allylic system. This p3 allyl complex has the metal sitting roughly at the middle of the triangle formed by the three carbon atoms of the allyl system, and at right angles to them, so that the orbitals of the metal may overlap with all three p-orbitals of the allyl group 24. This becomes a stable compound rather than an intermediate when M is a transition metal. 

The three p atomic orbitals of the allyl group combine to produce three tt molecular orbitals lAi, and 3 (Figure 7.10). The bonding MO (lAi) encompasses all the... 

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