Reaction dative coordination

Dative PSM involves the postsynthetic coordination of a metal center to one of the linker ligands. Examples of dative PSM reactions are summarized in Table 2. 

As shown in Table 4.38, three major reaction pathways are available to hypova-lent metals in the presence of an alkene (A) and (C) dative and synergistic coordination (B) carbocation formation and (D) and (E) metallacyclic and migratory insertions. The latter types are of particular importance in metal-catalyzed alkene polymerizations and will be given primary attention in the discussion that follows. 

The mechanism of reversible (5-hydrogen elimination from square planar lr(l) alkoxide complexes with labile dative ligands, followed by associahve displacement of the coordinated ketone or aldehyde by incoming phosphine, which can be implied in TH reactions, was proposed by Hartwig and coworkers [36]. 

B) In this case, a lone electron pair on oxygen forms a bond to Ff. A coordinate covalent bond (also known as a dative covalent bond) is a special type of covalent bond in which the shared electrons come from one of the atoms only. After the bond has been formed, its strength is no different from that of a covalent bond. Coordinate covalent bonds are formed when a Lewis base (an electron donor) donates a pair of electrons to a Lewis acid (an electron accepter) the resultant componnd is then called an addnct (a compound formed by the addition reaction between two molecules). The process of forming a dative bond is called coordination. 

Another example of a Bill compound is offered by the ligand VAPOL ( vaulted bisphenanthrol), which combines with AICI3 to form a three-coordinate complex, with no dative interactions. This compound will catalyze Diels-Alder reactions [64]. A five-coordinate compound, with two dative carbonyl bonds attached to the aluminum, has been postulated as the active intermediate in the catalytic reaction. 

The product of the reaction between a Lewis acid and a Lewis base is called an adduct. The bond between a Lewis acid and a Lewis base is called a dative or coordinate covalent bond. 

As in organic chemistry, diazoalkanes have found wide application as ultimate carbene sources. In contrast to the organic chemistry of diazoalkanes, however, the reactions do not proceed via free carbenes but rather via metal-mediated transformations of coordinated diazoalkanes. In some cases, diazoalkane complexes may be isolated (Figure 5.8). The parent diazoalkane, H2C=N2, has found somewhat less success in the synthesis of terminal methylene complexes LJM=CH2 however, this is primarily due to the lack of any kinetic (steric) or thermodynamic (71-dative) stabilization by carbene substituents. Thus methylene ligands... 

Several years ago, Seyferth [47] prepared complex 31 by reaction of 30 with Pd(PPli3)4 subsequently Akabori prepared the Pt analogue 32 and the dioxygen-palladium analogue [48]. In a similar manner, l,l -bis-(alkylthio)-ferro-cenes react with Pd(Bp4)2 (MeCN)4 in the presence of triphenylphosphine to give 33 [49, 50], results which reveal that formation of a dative metal-metal bond is not dependent on a macrocylic unit as part of the coordination sphere. The final set of... 

Summary Bulky monodentate ligands affect the structure and reactivity of siliconium ion complexes in several ways they enhance ionization, they promote a methyl halide elimination reaction, and they severely distort complex geometries. The latter effect enabled the assembly of a reaction coordinate model for the Berry pseudorotation, composed of crystal structures with varying NSiN and OSiO bond angles. In a competition between opposing effects of electron withdrawal by CF3 and steric bulk of a cyclohexyl ligand in the same molecule, a nonionic dissociation of the dative N->Si bond was observed. 

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