Divalent compounds containing coordination geometry

Zerovalent complexes of Pd and Pt are Pd( -alkene)(Bu -DAB) and Pt(cod)(R-DAB). Divalent Pd" and Pt" compounds are abundant. Key examples are five-coordinate PtCl2(R-DAB)(>j -alkene) and planar PtCl2(R-DAB). H and C NMR data showed that in the ground state the C=C skeleton of the alkene in PtCl2(R-DAB)( 7 -alkene) is in the trigonal plane. When a phosphine is in the plane of the alkene the compound, i.e. PtCl2(PR3)(R-DAB) contains monoden-tate R-DAB. This molecule is fluxional and the five-coordinate geometry is then an intermediate in the cr-N ct-N fluxional process. 

This result is consistent with the tetrahedral coordination exhibited by MT for most other divalent metal ions (67), a geometry that is not favored by d transition metals such as Pt(II). It is not yet clear that the increased levels of sulfhydryl-containing compounds in resistant cells is the cause of their acquired resistance or merely part of a more general response to stress. 

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