Tridentate chelate compounds

This variety of hypercoordinated bromosilicon compounds is in sharp contrast to hypercoordinated iodosilicon compounds, which are represented by far less crystallographicaUy evidenced examples. In addition to some pentacoordinated monoiodosilicon compounds with tridentate chelators (compound 177, Si—I bond lengths ranging between 2.74 and 2.82 A) [95, 188, 190], the first crystallographi-cally characterized hexacoordinated iodosilicon compound (with two Si—I bonds, 2.64 and 2.66 A) [203] has been reported very recently (compound 72, Scheme 15). 

Mononuclear Fe(ll) Spin Crossover Compounds of Tridentate Chelating 1,2,4-Triazole Derivatives... 

For synthesizing tris-chelates (or bis-tridentate chelates) the ideal source material is RuC13 3 H20 simply because of its availability. Hypophosphite reduction in the presence of the ligand provides a fairly general, rapid synthetic technique. While there will always be questions of purity for compounds prepared by this route, it is a valuable method for the initial synthesis of a compound to determine general properties before exploring other synthetic routes. 

The fundamental prerequisite for the applicability of this technique is the necessity of (usually bidentate or tridentate) chelation properties of both the chiral SO and the SA. This requirement is fulfilled by compounds having two polar functional groups in a favourable arrangement to each other, like a/p-amino acids, amino alcohols, a-hydroxy... 

The first complexes of a-keto ylides and group 5 early transition metals have only recently been obtained by reaction of Nb(III) derivatives [[NbCl3(dme) (R C=CR")] with 25 (R = thiazolyl) (Scheme 16). The chelation of the ylide occurs through an N,0-coordination to the metal center and in presence of MeLi a deprotonation of a phenyl ring takes place with the loss of alkyne, leading to the formation of a new orfho-metallated binuclear compound 32. The two ylides involved in the complexation behave as tridentate anionic ligands and are mutually in a trans disposition in order to minimize the steric hindrance [71,72]. Another binuclear niobium complex 33 has been obtained from 25 (R = Me, Ph) with this time an 0-coordinated a-keto ylide [68]. 

---