Reaction surveys

A variety of mechanisms may participate in the displacement reactions surveyed above. Some displacements, including tosylates and some epoxide ring openings, occm with the high degrees of inversion of configmation expected... 

Mention has already been made of the publications of Kerr and Moss [23] as a source of bibliography. The same works list information on the kinetics of the reactions surveyed. Although the information is not critically evaluated and is now slightly dated, the coverage is broad, and where no evaluation of data on a particular reaction is available, the Kerr and Moss collection provides a valuable source for the existing data as does the NIST database [22], also discussed in Section 3.3. This too lists the kinetics data and also provides a graphical presentation. 

Le Roux, C., Dubac, J. Bismuth(lll) chloride and triflate novel catalysts for acylation and sulfonylation reactions. Survey and mechanistic aspects. Synlett2002, 181-200. 

We conclude our reaction survey with Scheme 4-66, which summarizes the known reactivity characteristics of metal-alkyne complexes. 

In the absence of noticeable strain in the metallacycle, Z)/7°(M-C) Z)/7°(M-C)i. Therefore, (JA)ptDH° (Gj-H) — Z)//°(M-C)2 —Z)/7°(M-H), a balance that is similar to the one made for the intermolecular C-H activation (reaction (60)). In the present case, however, the weight of the entropy term is expected to be smaller than for reaction (60), —44kJmoP . As entropy effects are responsible for many thermodynamically unfavorable reactions surveyed in Section 1.22.5.2, it is thus not surprising that cyclometallations are so common and that they often compete with intermolecular C-H activations. 

It should be pointed out that some Pd-catalyzed reactions of allenes with nucleophiles proceed by a different mechanism. The mechanistically interesting intramolecular reaction of allenylcarbamate 105 with acrolein afforded the oxazolinone 106 in the presence of Pd(OAc)2 and LiBr. This reaction is promoted by Pd(II), not by Pd(0) [31]. Unlike the Pd(0)-catalyzed reactions surveyed in the above section. 

In addition to the continuous hydrofomiylation reactions surveyed so far, the following section gives a short description of rhodium-catalyzed carbonylation, which is mechanistically related to hydroformylation as the essential steps in the catalytic cycle, for example, the insertion of carbon monoxide into an organic substrate, are similar. 

On the other hand, a considerable number of carbene complexes based on derivatives of pyridinylidenes (168) and their analogues in the quinoline (169 and 170) and acridine series (not shown) were prepared and tested in Mizoroki-Heck reactions [221], These ligands involve carbenes, which have a carbene core almost isostructural to the one in complex 167. In the test reactions surveyed, an almost identical performance in type 1 and type 2 processes was observed, the latter being dramatically inferior to the perfonnance of 167 (Table 2.8, entries 7-11) [221]. This, as well as the absence of any structural dependence on the performance, clearly indicates the slow-release operation. 

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