Regarding the diamagnetic components in Rosenberg’s “platinum pyrimidine blues”: Species in the cis-Pt(NH3)2-1-methyluracil system

On the Heterogeneous Nature of Cisplatin‐1‐Methyluracil Complexes: Coexistence of Different Aggregation Modes and Partial Loss of NH3 Ligands as Likely Explanation

“…As to the H5 doublet at 5.835 ppm, seen in the spectrum immediately after dissolving the evaporated sample in D 2 O (Figure 6 (a)), it is close to resonances of μ‐1MeU species ( 4 and possibly 5 ) rather than to terminal (1MeU‐ N3 ) ligands, which are upfield by some 0.15–0.25 ppm. Its H6 counterpart at 7.38 ppm (established by 1 H, 1 H‐COSY [4] ) is likewise close to H6 of 4 , which is at 7.40 ppm. We propose that these signals correspond to a trinuclear complex ( 6 ), as it is only seen in concentrated solutions and, according to a DOSY spectrum (DOSY= D iffusion O rdered S pectroscop Y ), is larger than the head‐tail dimer 4 .…”

“…The removal of halide ligands from Pt II complexes by means of a silver salt is a common procedure employed in preparative Pt chemistry. In earlier reports on related simple complexes with 1‐methylcytosine (1MeC) [2] as well as 1‐methyluracil ligands [3,4] we have provided ample evidence how true the above statement can be. Besides the planned and expected main products in seemingly straightforward reactions also a multitude of minor products are formed, which in large part remain poorly characterized or not characterized at all.…”

“…As indicated in Scheme 3, condensation reactions can take place in different ways, leading altogether to five different products, (A)–(E). We assign the H5 signal at 5.64 ppm to the μ‐hydroxido species cis‐ [(NH 3 ) 2 (1MeU)Pt(μ‐OH)Pt(1MeU)(NH 3 ) 2 ] + ( 3 ), which corresponds to product (A) in Scheme 3, based on its chemical shifts [4,13] . Much to our surprise, 1 H NMR signals of the well‐known head‐tail dinuclear complex cis‐ [Pt 2 (NH 3 ) 4 (1MeU‐ N3,O4 ) 2 ] 2+ ( 4 ) [16] , hence condensation product (C) in Scheme 3, are absent in this spectrum.…”

“…Both compounds have three ligands capable of undergoing such reactions: H 2 O/OH − , 1MeU − , and NH 3 . There is ample structural evidence for the existence of μ‐OH, μ‐1MeU, and μ‐NH 2 bridges in Pt II coordination chemistry [4,20,38] . Scheme 5 summarizes the various possibilities relevant to 1 b and 1b’ .…”

Formation of Cisplatin Adducts with the Epigenetically Relevant Nucleobase 5‐Methylcytosine

“…[ 1a ] Only recently, some of the components present in platinum 1‐methyluracil blues were elucidated. [ 18 ] Apparently, only 5 % of the product mixture consists of a presumably polymeric species being responsible for the blue color and the paramagnetic properties. This illustrates the high complexity of platinum nucleobase chemistry.…”