Tetradentate derivative

Most complexes with catalytic properties are tetradentate derivatives of salen but other ligands, e.g., A-(hydroxyphenyl)salicyldimine and A-(hydroxyphenyl)pyridine-2-carboxaldimine, form ternary complexes with bipy and CU ((14) and (15), respectively) that are catalytically competent. 

The interesting observation, unexpected on the basis of limited published data of a tetradentate derivative of L8 249 250 but in full agreement with the MM analysis is that the stabilities do not follow the usual Irving-Williams behavior (Co2+ < Ni2+ < Cu2+ > Zn2+)251 252 but that L4 is zinc(II)-selective. This was interpreted as a combination of the steric effects discussed above, electronic effects (distorted coordination geometries, misdirected valences), which are unimportant for the d10 ion zinc(II), in contrast to copper(II), especially nickel(II) and smaller metal ions such as cobalt(III).78... 

The first heterodifunctional ligand derived from a tetradentate phosphine was made in a study concerning synthesis and characterization of a sjransj is-], 3-bis(diphenylphosphino)-2,4-bis-(diphenylphosphinothioyl)cyclobutane and its complex with PdCl2.257... 

A new class of oxidation catalysts is prepared by complexation of metal-Y zeolites with tetradentate N,N -bis(2-pyridinecarboxamide) derivatives (Scheme 7.3). 

The branched tetradentate ligand tris(2-aminoethyl)amine (tren) forms rather stable metal complexes with most transition metal ions. It is a very hard and basic ligand and consequently its iron(II) complexes are all high-spin. Later we will discuss hexadentate derivatives of this ligand which form crossover complexes (see Sect. 3.2). 

The most common tetradentate Schiff base ligands used are Salen (where H2Salen = A,A -ethylene-bis(salicylideneamine) and its derivatives (see (Figures 3, 18 and 19) for structures). 

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