Alkylation reaction tetradentate ligands

Cobalt complexes with square planar tetradentate ligands, including salen, cor-rin, and porphyrin types, all catalyse the reduction of alkyl bromides and iodides. Most preparative and mechanistic work with these reactions has used cobalamines, including vitamin-B,. A generalised catalytic cycle is depicted in Scheme 4.10 [219]. At potentials around -0.9 V vs. see, the parent ligated Co(lll) compound un-... 

The tetradentate ligand forms monomeric square planar complexes. Synthetic and kinetic studies reveal that the coordinated mercapto group may be converted into the coordinated thioether function without breaking the metal-sulfur bond. The nucleophilic power of the coordinated mercapto group exceeds that of RSH, but depends on the metal atom. Bridging protects the sulfur atom from alkylation. In the case of nickel(ll), alkylation is accompanied by expansion of the coordination number of the nickel from 4 to 6. Ligand reactions have led to the synthesis of planar ligands completely cydized about the metal ion. 

In your reaction, the aldehyde R group is aromatic (2). Aromatic R groups produce more stable imine products than do alkyl R substituents. Salpd is a tetradentate ligand it contains four atoms, two N and two O, that can readily bind to a metal ion. Metal complexes containing multidentate ligands show enhanced stability over those with analogous monodentate donors. Bjerrum first noted the enhanced stability of five-membered rings... 

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