Associative path c

The reductive elimination process induced by phosphine-coordination has been observed also for ct5-NiR(CN)L2 type complexes [36], 

Path (a) is discussed in Chapter 8. On the other hand, path (b) was extensively studied by Kurosawa et al. using a series of M(allyl)(Ar)L complexes (M = Ni, Pd), and the following mechanistic features emerged [42,43]. 

5)(PPh3) proceeds 26 times faster than that of Pd(7t-allyl)(C6H3Cl2-2,5)(PPh3). The platinum analog is totally inactive under the same reaction condition [43b]. 

It has been further documented that the rate of reductive elintination from Pd(jr-methallyl)Ar(olefin) complexes increases as the jt-acidic nature of the olefin ligand increases (Table 9.5) [43c], The olefin-coordinated jt-allyl complex has been postulated as a key intermediate for rate acceleration by added olefins in the reductive elimination from Pd(jt-allyl)(R)L complexes (L = PPh3, AsPPhs) [43c,45], 

Rate of reductive elimination for Pd(/7 -methallyl)(C6HCl4)(olefin) 

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Associative path (c) has been mainly observed for nickel(II) complexes [BOSS], This is because nickel(II) has a higher propensity to make five-coordinate species than palladium(II) and platinum(II). A steric condition is another important factor. Thus the reductive elimination from bipyridine-coordinated dialkyl-nickel complexes is known to be effectively accelerated by addition of n-acceptor olefins such as maleic anhydride and acrylonitrile to the systems (Scheme 9.8)... 

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