Oliver Renn

Rhodium(I) complexes of the type [Tp3R,5RRh(LL)] (LL = 2 CO, NBD, COD) with trifluoromethyl substituted tris (pyrazolyl) borate ligands and their dynamic behaviour in solution. The X-ray crystal structure of TpCF3MeRh(CO)2☆

Three seriesof Rh(I) complexes of the type Tp3R,5RRh(LL), with LL = 2 CO (1), norbornadiene (NBD) (2) and 1,5-cyclooctadiene (COD) (3) and the tris (pyrazolyl)borate (Tp) ligands 3R=5R=Me (a), 3R=CF35R=Me (b); and 3R=5R=CF3 (c) were synthesized and fully characterized by IR and multinuclear NMR spectroscopy. Three isomeric forms were identified in solutions of these complexes: two square-planar isomers with a κ2-Tp3R,5R ligand, the uncoordinated pyrazolyl ring occupying either an equatorial position (type A), or an axial position (type B), and a five-coordinate species with a κ3, Tp3R,5R ligand (type C). In the carbonyl complexes 1 the dynamic equilibria between these isomers are solvent dependent. Interestingly, solutions of complex 1c contained all three isomers simultaneously. 103Rh and 13C NMR spectral studies indicate that the NBD compounds, 2, preferentially form square-planar complexes when TpCF3,Me and TpCF3,CF3 are present, while for the COD complexes, 3, square-planar complexes are preferred for all three Tp-type ligands. The X-ray structure of TpCF3,MeRh(CO)2 (1b) was determined (spacce group C2/ c,a = 21.271(9), b = 11.004(3), c = 21.563(9) A, β = 114.93(3)°, V=4577(3) A3, Z = 8, R = 3.41, Rw = 4.70). Its structure is of type B, with the third pyrazolyl ring axially placed, the N(4) being almost directly above the Rh atom but exerting only a weak Rh-N interaction.

A mixed Pt2Tl complex of 1-methylthymine: structural evidence for the stereoactivity of the TlI electron lone pair and unexpected intracomplex nucleobase stacking

Abstract A trinuclear PtIITlIPtII complex with bridging 1-methylthyminato (1-MeT) nucleobases, cis-[(NH3)2Pt(1-MeT)2Tl(1- MeT)2Pt(NH3)2]NO3·7H2O, has been prepared and structurally characterized. It crystallizes in the space group C2/c with a=17.854(4), b=23.063(5), c=11.813(2) A, β=94.90(3)°, V=4846(2) A3, Z=4. The structure was refined on 3949 reflections to R=0.0448, Rw=0.0564. PtII binding is through the N3 positions of the 1-MeT rings, while TlI is bound via four exocyclic O4 oxygens. PtTl separations (3.085(1)A) are sufficiently short to postulate bonds between the two metals. The compound, which represents a rare example of a d8-s2-d8 metal assembly, displays structural features indicative of a stereoactive electron lone pair at the central TlI. Unlike all previously studied related PtIIMPtII complexes, for the first time intramolecular stacking between two of the four nucleobases is observed. This fact and the cleft at the TlI appear to be interrelated.

Metal-stabilized rare tautomers of nucleobases 3. (1-methylthyminato-N3) (1-methylthymine-N3)-cis-diammineplatinum(II) hemihexachloroplatinate(IV) dihydrate

Abstract The crystal structure of cis-[(NH3)2Pt(1-MeT)(1-MeTH)][PtCl6]0.5·2H2O, where 1-MeTH=neutral 1-methylthymine, C6H8N2O2, and 1-MeT is the corresponding anion, is reported. The compound contains both heterocyclic bases bound to Pt via the N3 positions, with the neutral 1-MeTH protonated at 04. It hence represents the rare enol tautomeric structure of this nucleobase. The compound crystallizes in the space group P21/n with cell dimensions a=11.814(4), b=13.270(3), c=14.738(3) A, β=74.02(2)°, Z=4.

Simultaneous binding of soft and hard metals to a pyrimidine nucleobase: trans-K2[PtI2(1-MeU)2]·6H2O, an anionic Pt-1-methyluracil (1-MeU) complex arranged in circles

The anionic complex trans-[PtI2(1MeUN3)2]2− (1-MeU=1-methyluracil anion, C5H5N2O2), as its K salt, forms a supramolecular assembly with anionic entities linked via K+ cations and bridging H2O molecules. The Pt coordination sphere is normal square-planar. Crystallographic data are as follows: C10H22I2K2N4O10Pt, rhombohedral, space group R3, a=26.166(4), c=9.245(2) A, U=5482(3) A, Z=9. The structure was refined to R=3.46, Rw=4.63 for 1813 unique reflections with I>3σ(I).

A model compound for the interaction of thallium(I) with nucleobases:crystal and molecular structure of (nitrato)(1-methylcytosine)thallium(I)

The reaction of 1-methylcytosine with TINO 3 in variable ratios gave crystals of the 1:1 complex, TI(C 5 H 7 N 3 O)NO 3 . The crystal structure of the title compound, which represents the first example of a nucleobase complex with TI(I), has been performed. C 5 H 7 N 4 O 4 TI crystallizes in the triclinic system, space group Pi , with cell dimensions a = 3.786(2), b = 10.804(5), c = 11.508(5) A, a = 105.02(3), β = 92.37(4), γ = 98.24(4)° U = 448.4(4) A 3 , Z = 2.

The x-ray structure of cis-bis(cyclopropylamine)bis(1-methylthyminato-N3)-platinum(II) dihydrate, cis-(cpa)2Pt(1-MeT)2·2H2O, and chemistry related to ‘platinum thymine purple’

Abstract The crystal structure of cis-(cpa)2Pt(1-MeT)2·2H2O (1) with cpa = cyclopropylamine and 1-MeT = 1-methylthymine anion (C6H7N2O2), is reported, 1 crystallizes in the monoclinic system, space group P21/c, with a = 10.645(2), b = 14.878(3), c = 15.535(3) A, β = 106.44(3)/dg, V = 2359.8 A3, Z = 4. Pt coordination to the 1-MeT rings is through N3 each with the two 1-MeT rings oriented head-head. Thus 1 can be considered a realistic model of a hypothetical cross-link of two thymine bases of DNA by a cis-a2Pt(II) moiety. As shown by 1H NMR spectroscopy, 1 loses both cpa and 1-MeT ligands in acidic medium. Likewise, cis-(cpa)2PtCl2 undergoes solvolysis in aqueous solution with liberation of cpa. Starting with 1, dinuclear complexes of composition cis-[(cpa)2Pt(1-MeT)2Pt(NH3)2]2+ (2), cis-[(cpa)2Pt(1-MeT)2Pt(cpa)2]2+ (3) and cis-(cpa)2Pt(1-MeT2PtCl2 (4), as well as a purple, mixed-valence compound of unknown composition were prepared. The ‘purple’, which originally was derived from cis-(cpa)2PtCl2 and 1-methylthymine, was reinvestigated and, based on ESCA data, is assigned a Pt oxidation state between 2 and 3 rather than 3.75 as proposed before.

Formation and X-ray crystal structure analysis of a Pt(IV) complex of 1-methylthymine, obtained through Au(III) treatment of a Pt(II)complex

Abstract The crystal structure of cis,cis-[(NH3)2Pt(1-MeT)2(OH)(H2O)]AuCI4·H2O, where 1-MeT is the anion of 1- methylthymine, C6H7N2O2, is reported. The compound contains both heterocyclic bases bound to Pt via the N3 positions, the two nucleobase ligands being in a head-to-head orientation. It represents the first X-ray structurally characterized example of a Pt(IV) species of thymine. The compound crystallizes in the space group P 1 with unit cell dimensions a=8.435(4), b=11.884(3), c=12.869(7) A, a=97.28(3), β=91.66(5), γ=110.66(5), V= 1193(2) A3.

Platinum coordination chemistry with nucleobases

Synthetic, structural and reactivity aspects of metal complexes of Pt, Pd and Au, containing t he p yrimidine nucleobases I-methyluracil and I-methylthymine, are repor- ted. A particularly rich coordination chemistry is found within the *-A Pt system (A = NH3 or A2 = chelating diami- ne) and attribu?ed to a combination of favorable geometry (relative positions of exocyclic oxygens of pyrimidine bases adjacent to the Pt binding site N3), high basicity of these sites, and ready oxidizability of Pt(I1). Examples discussed include mixed-nucleobase c omplexes, dinuclear Pt(I1) comple- xes, mixed-metal complexes, and mixed-valence state com- pounds.

Modelling Platinum-DNA Interactions

The understanding of the effects of a small molecule such as cis-diamminedichloroplatinum(II) (Cisplatin, cis-DDP) on a biomacromolecule, e.g. DNA, or on the biology of a whole cell starts with the molecular level. Model studies at various degrees of complexity — with isolated model nucleobases, nucleosides, nucleotides and oligonucleotides1–8* — have greatly contributed to our present understanding of metal-DNA interactions in general and those of cis-DDP and DNA in particular. Despite obvious limitations and shortcomings, work with isolated model nucleobases is meaningful in that fundamental questions such as binding patterns and ligand rotation processes may be conveniently studied. In the following, mainly results from own studies on the interactions of mono-and difunctional Pt electrophiles with N1 methylated pyrimidine nucleobases (1-methylcytosine, 1-MeC or C, 1-methylthymine, 1-MeTH or TH, 1-methyluracil, 1-MeUH or UH) and N9 alkylated purine nucleobases (9-methyladenine, 9-MeA or A, 9-methylguanine, 9-MeGH or GH, 9-ethylguanine, 9-EtGH or GH) will be discussed**.