Hexacoordinate lead complexes chelate

A convenient method for the preparation of neutral bis(N->Si) hexacoordinate silicon complexes has been developed and reported recently, consisting of ligand exchange between a polychlorosilane (1) and 0-trimethylsilyl derivatives of hydrazides (2, Eq. 1) [2]. An attempt to utilize this synthetic route for the preparation of isomeric 0->Si coordinated chelates did not lead to the expected hexacoordinate complexes, but to ionic siliconium chloride salts stabilized by two (O—>Si) dative bonds (5, Eq. 2) [3]. 

Complexation of the well-known dithiocarbazate chelate ligand (DTCA ) with Al3+, Sn2+, and Sn4+ ions leads to the formation of hexacoordinated complexes with 1 1 (M + DTCA) ratio, which were investigated for antimicrobial activity <2001SRI115>. These compounds, however, were found to be thermally unstable. 

At the same time, according to x-ray data for zinc chelate 909, the nitrogen atom is turned to the side of the metal. The distance Npy-Zn is 2.80 A, that allows us to consider the possible participation of the examined donor center in binding with the metal, leading to formation of a hexacoordinated structure (two-capped tetrahedron) [243]. In relation with this result, let s pay attention to the data reported in Refs. 244 and 248. The tetrahedral configuration without coordination of the nitrogen atom of pyridine is attributed to the cobalt complex 907 (X = NTs, M — Co), although this N atom is rotated to the side of the metal [244]. The pentacoordinated complex 910 is described in Ref. 248, in which only one pyridine substituent is coordinated (the distance Npy-Co is 2.45 A) ... 

In search for new oligomers and polymers containing hypervalent silicon chelates, the reactions of bis(trichlorosilyl)ethane (1) with O- and N-trimethylsilylated hydrazides (2 and 3, respectively) have been studied. The reaction of 1 with 3 was reported to lead to ionic binuclear disiliconium dichloride salts (4, Eq. 1) [1]. It was not obvious how the reaction of 2 with 1 might proceed would it form a neutral binuclear hexacoordinate complex, like the mononuclear analogues [2], or would it form ionic complexes, in analogy to 4 ... 

For the corresponding hexacoordinate tris chelated complex Cr(en)i, the initial photoreaction leads to substitution at one of the coordination positions to give Cr(en)2(enH)(H20). This photoreaction involves dissociation of one end of a coordinated ethylenediamine, followed by protonation of the nitrogen on the free hinged ethylenediamine arm of the chelate... 

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