Binuclear coordination compounds formation

Among molecular complexes recently obtained by the ligand-exchange method we emphasize the coordination compounds of diorganoditellurides. Thus, the interaction (3.128) of molybdenum hexacarbonyl with diphenyltelluride in THF leads to the formation of a binuclear complex 705 [272] ... 

In nickel and palladium dithiobenzoato complexes, four-membered chelate rings are formed (366), whereas, in the corresponding phenyl-dithio acetates [M2(S2CCH2Ph)4], the dithio ligands act as bridging groups between the two metal atoms, with the formation of binuclear units (367). The molecular structure of the latter compounds shows that each metal atom is coordinated to four sulfur atoms and to the other metal atoms in a square-pyramidal geometry. Other evidence for... 

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]. 

Binuclear platinum complexes with the o -pyridinato ligand can be formed with the metals in a divalent oxidation state. Two such complexes are the head-to-tail dimer [Pt(QH4NO)(NH3)2]2+ and the head-to-head tetramer [Pt2(CsH4NO)2(NH3)4]2+. This tetrame-ric platinum(II)-(II) compound is prepared under experimental conditions where the pH is kept around neutrality to avoid the formation of the partially oxidized complex.1120 Platinum-195 NMR spectroscopy can be used to show that the head-to-head to head-to-tail isomerization of these complexes involves dissociation of one ligand arm followed by an intramolecular linkage isomerization. Finally bond formation occurs between the divalent platinum with the vacant coordination site and the uncoordinated end of the ligand.1121... 

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