Ligand-exchange reaction identity

DMSA is present in the "mTc-succimer (MediPhysics, Inc.) kit as a 90 10 meso d, 1 isomer mixture. The structure and identity of the 99mTc-species produced in this formulation has not been definitively resolved. The complex(es) formed is (are) believed to contain 99mTc in an oxidation state(s) below five and has been referred to as 99mTc(III) DMSA [66,67], Because of the possibility of multiple complexes, it has been impossible to elucidate the mechanism of localization however, it is reasonable to assume that after GFR, some of the agent is reabsorbed by tubular cells and retained by ligand exchange reactions, in which "mTc becomes bound to SH-containing cytoplasmic proteins [67,68]. 

The dipalladium organyls 51, derived from 49 (M = Pd, X = C1) by ligand exchange reaction between the bridging group and acetylacetonate, are not mesomorphic in their pure state, but form mesomorphic charge transfer systems with the electron acceptor TNF [95]. The identity of the induced mesophase is still unknown, but seems very likely to be columnar [96]. Furthermore, lyotropic nematic phases were obtained in the ternary mixture 51/TNF/linear alkane (the binary mixture 51/alkane did not yield mesomorp-hism). The nematic phase in this system is though to have a columnar nature, namely a nematic columnar phase. 

The compound [space group 7 3, a = 32.719 (1), c = 73.567 (2) A] is obtained by a ligand exchange (30 CHaCOO by 30 H2PO2 ) reaction. The IR spectrum is practically identical to that of compound A except for the appearance of H2PO2 bands [1118 (m), 1075 (w), 1033 (m) cm ] instead of CHsCOO bands. Also the Raman and electronic absorption spectra are almost identical to those of compound A. 

Besides rearrangements, ligand exchange, formation of alkanes, alkenes and other products, release of cyclopropanes is one of the most important reactions of metallacyclobutanes. Of course, this latter reaction is only useful in cyclopropane synthesis if the product is not identical with the starting material used to form the metallacyclobutane. Nevertheless, the discovery of a complex formed from hexachloroplatinic acid and cyclopropane and later structural elucidations have initiated intensive investigations on the conversion of cyclopropanes to metallacyclobutanes and release of cyclopropanes from the latter. These results have been thoroughly discussed in several reviews. " Therefore in this section only some general aspects of cyclopropane formation from metallacyclobutanes and selected synthetically useful methods are discussed. 

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