Cytosine nucleobase as a tridentate ligand: Metal binding to N3, N4 and O2 in the trinuclear complex cis-[Pt(NH3)2(mcyt)2{Pd(en)}2][NO3]4·H2O (mcyt = 1-methylcytosinate, en = ethane-1,2-diamine)

Reactivity of Ammonia Ligands of the Antitumor Agent Cisplatin: A Unique Dodecanuclear Pt4,Pd4,Ag4 Platform for Four Cytosine Model Nucleobases

“…While Pt À N and Pd À N bond lengths agree with expectations, [14] both the Ag À O and Ag À N lengths are significantly longer than in a mixed Pt,Ag complex of 1,5-dimethylcytosine, [15] in which they amount to 2.259(8) and 2.16(1) (average), respectively. The binding of the Ag1 and Ag1' atoms is special in that all four of the surrounding d 8 metal ions, that is, Pd1, Pt1, Pt2, and Pd2 (for the case of Ag1), appear to be involved in weak donor!acceptor bond formation with the Ag (11) ) are longer than those in typical donor-acceptor bonds between such metals, [12b, 17, 18] yet the number (four) of such interactions is larger in the present case.…”

“…+ ion binding to the O2 position of N3,N4-metalated cytosine nucleobases has been observed before, [14,15] and the reversal of the chemical-shift changes upon addition of Cl À ions to a solution of 10 (see below) further supports this view.…”

“…[13] Fourth, the chemical shifts of the cytosine resonances in X, which are upfield (by approximately d = 0.6 ppm for H6, d = 0.2 ppm for H5, and d = 0.2 ppm for CH 3 ) from those of 6 and 8, are likewise indicative of metal binding to the anionic cytosine nucleobase through the N3 and N4 positions. [14] According to this proposal, the initial anchoring site of the Pd II species is the aqua ligand of the Pt complex 6 rather than the heterocyclic nucleobase. As the exocyclic amino group of 1-MeC does not provide a lone electron pair for metal binding, as in the case of 2-aminopyridine or pyrazolate ligands (see Scheme 1 and reference [3]), Pd II coordination to this site is not possible unless it has lost a proton.…”

“Directed” Assembly of Metallacalix[n]arenes with Pyrimidine Nucleobase Ligands of Low Symmetry: Interchanging Metals in Mixed‐Metal Metallacalix[4]arenes and Incorporating Additional Metals at the Exocyclic Groups

“…[21] Given the fact that Pd-Pd distances of even > 3.0 have been demonstrated to display weak metal-metal "interactions", [20c] it is likely that the Pd 3 stacks in 6 display significant metal À metal bonding, albeit not to the same extent, as seen in dinuclear complexes with Pd III À Pd III single bonds. [22] The 1 H NMR spectrum of 6 in D 2 O is shown in Figure 13 When an excess of NaCl was added to a solution of 6 in D 2 O, the formation of new sets of resonances due to unknown species was observed.…”

Pt as Mediator of Strong Antiferromagnetic Coupling between Two CuII Ions in a Heteronuclear CuIIPtIICuII Complex of the Model Nucleobase 1-Methylcytosinate

“…[3] In a limited number of cases the stoichiometry of the trinuclear species was inverted, that is PdM 2 , [4] Pt 2 M, [5] or PtM 2 [6,7] compounds were formed with L acting as tridentate ligands (Scheme 1, c)). Scheme 1.…”