Pyrimidines transition metal complexes

Transition Metal Complexes of l-(2-Methylphenyl)-4, 4, 6-Trimethyl Pyrimidine-2-thione Synthesis and Biological Studies... 

Osmium Tetroxide-Pyridine. Osmium(VI) tetroxide is one of the most extensively used probes for DNA structure. It is an example of a high-valent transition metal complex which, due to its uniquely reactive center, is able to functionalize specific bonds on DNA. This powerful oxidant is known to form cisoid osmate esters upon attack of an electron-rich double bond. By tuning the reactivity of OSO4 and its esters with the addition of other ligands, it has been possible to generate a family of reactive probes for exposed pyrimidine bases. 

The following Table (Table 1) shows the values of the stability constants of some purines and pyrimidines with a number of transition metal ions (7, 2, 36, 69). Procedures for the synthesis of Cu, Co and Ni complexes with pyrimidines have been reported (65, 92, 93). The preparation of purine-metal compounds are described elsewhere (94, 95). There seem to be great difficulties in the quantitative study of metal complex formation, especially with the free purines, since the resulting metal chelates are almost insoluble in aqueous solution. Therefore, dioxane-water mixtures have been employed in a number of experiments. 

The trend in the few examples where an NHC is functionalised with a sulfur-containing group does not necessarily reflect the choice of scaffold seen above, but the S functionalised NHC ligands do, in part, follow the general development of an S/P exchange in conventional functionalised phosphanes. The other major source for S functionalised NHC complexes of transition metals is the replacement of sulfur by a transition metal in certain Ji-sulfurane compounds. The NHC ligand, a tetrahydro-pyrimidine derivative, is only liberated during the reaction of the sulfurane with the transition metal precursor. 

The spectra of (M3l5RuClII) -nucleoslde complexes Invariably exhibit fairly Intense UfCT transitions, which are well resolved from the intrallgand banc s and provide a convenient probe Into the nature of these metal-nucleoside Interactions (12-14,IJ). Reference to Figure 6 reveals that these absorptions are usually localized In two distinct regions of the spectrum, one in the near UV and the other in the visible. The energy of these bands Is primarily dependent upon the particular purine or pyrimidine Involved,... 

---