Tripodal tetradentate

In order to construct new types of binding and activating models of dioxygen molecules, Jitsukawa, Masuda and their co-workers have synthesized a novel group of tripodal tetradentate ligands and successfully utilized them in the formation of mononuclear copper(II) complexes with novel structural features (complexes (473)-(488)).395-403 This group of ligands has four... 

When one starts with nickel(II) salts of poorly coordinating anions such as hydrated Ni(BF4)2 and Ni(C104)2, and with the tripodal tetradentate ligands with phenyl substituents on the donor... 

When triethanolamine H3L13 (35) was reacted with sodium hydride and iron(III) chloride, the hexanuclear centrosymmetric ferric wheel [Nac Fe6(L13)6 )Cl (36) was isolated. Amidst a set of possibilities in the template-mediated self-assembly of a supramolecular system, the one combination of building blocks is realized that leads to the best receptor for the substrate [112]. Therefore, the six-membered cyclic structure 36 is exclusively selected from all the possible iron triethoxyamine oligomers, when sodium ions are present. The iron(III) complex 36 is present as an Sg-symmetric wheel, with an encapsulated sodium ion in the center and a chloride counterion. Consequently, the trianion (L13)3- acts as a tripodal, tetradentate, tetratopic ligand, which each links three iron(III) ions and one sodium ion. In the presence of cations with different ionic radii, different structures are expected. Therefore, when triethanolamine H3L13 (35) was reacted with cesium carbonate and iron(III) chloride, the octanuclear centrosymmetric ferric wheel [Csc Fe8(L13)8 ]Cl (37) was isolated (Scheme 13) [113]. 

Thiosemicarbazidodiacetic acid (H2L) (124) reacts with RhCl3 3H20 in ethanol in the presence of Lewis bases (B), forming [Rh(L)(B)Cl] H2O (B = OH-, py, a picolone, PPh3, aniline) in the presence of bipy or phen (NN), the product is formulated as [Rh(L)(NN)]Cl.1105 Examination of models and IR analysis suggest that the thiosemicarbazide diacetic acid acts as a dianionic tripodal tetradentate, bonding to the Rh through two O, an N and an S atom. 

Nb and Ta derivatives are hard acids and then-complexes with P- or As-donors are limited. Tertiary phosphines, especially PMes, have been widely used to stabilize low-valent derivatives. C-H activation reactions, promoted by the formation of thermodynamically stable Ta-H, Ta-C, and Ta=C bonds have resulted in metallacycles based on unusual anionic phosphorus donors. Nucleophilic Ta phosphinidene complexes could be stabilized by a tripodal tetradentate [NN3] amido ligand. The terminal PR ligand reacts smoothly with aldehydes, providing a general synthesis of phosphaalkenes RP=C(H)R and act thus as a phospha-Wittig reactant see Phosphorus Organophosphorus Chemistry). 

Binuclear zinc complexes wherein each metal center is supported by a tripodal tetradentate ligand environment involving a bridging phenolate donor are reactive toward tris(4-nitrophenyl) phosphate and bis(4-nitrophenyl) phosphate in ethanol/ water.234 The pH-rate profile studies of these reactions are consistent with a mechanism that involves the formation of a reactive mononuclear zinc hydroxide species via cleavage of the binuclear solid-state structure. This mononuclear Zn-OH species is proposed to act as the nucleophile toward the phosphate ester substrate. 

Fig. 48 Tripodal tetradentate ligands having internal hydrogen-bond donor amine substituents.

The introduction of a tripodal tetradentate ligand such as tren or tmpa on the aqua Cu(II) ion induces a changeover in the water exchange mechanism [52-54]. Complex-formation reactions of these complexes exhibited a similar trend. Volume profiles for the complex-formation reactions (with pyridine) of [Cu(tren)H20] and [Cu(Me3tren)H20] + (Mestren is momomethylated on each primary amine... 

Masukazu H, Masuaki K, Yuzo Y. Mononuclear and mixed-valence trinuclear manganese complexes containing tripodal tetradentate ligands. Phenolato, carboxylato, and alkoxo bridges. Bull Chem Soc Jpn 1997 70 649-57. 

Fig. 27 X-ray structures of tripodal tetradentate click complexes 117 (a) [214] and 119a (b) [216], Hydrogen atoms and non-coordinating counter ions have been omitted for clarity...

Scheme 19 Synthesis of tripodal tetradentate click cranplexes (/) CUCI2, MeCN (h) [Cu (MeCN)4]BF4, MeCN (Hi) 1 eq Co(C104)2, MeCN, RT, 2 h (iv) for 119a 0.5 eq Co(C104)2, MeCN, RT, 2 h for 119b 0.5 eq Co(C104)2, MeOH, reflux, 1 h for 119c 0.5 eq Co(C104)2,...

The cadmium(ll) chelate of the tripodal tetradentate ligand tren also yielded the mixed-ligand complex cation of the salt [Cd(tren)(xan)]C104 H20 [29], where the metal ion is only five-coordinated and the anionic xan ligand forms the Cd-N7 bond (2.224 A) reinforced by the intramolecular interligand H-bond (tren)N-H" 06 (2.889 A, 117.6°). In the compotmd traui-[Cd(theo)2(H20)4]-2DMF [30], each theophilinate(l-) anion binds the cadmium(ll) center by the Cd-N7 bond (2.300 A) in cooperation with an intramolecular H-bond (aqua)0-H - 06 (2.689 A, 158.5°). 

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