Platinum—Terpyridine Complexes

The X-ray crystal structure of a [Pt(terpy)Cl]—AMP complex has also been briefly reported [59]. In this case, the complex consists of a hydrogen bonded AMP base pair, that mimics the rare Hoogsteen model [60] with NH2—Ni and NH2—Ny hydrogen bonds (see Appendix 1) sandwiched between two platinum—terpyridine molecules. The nucleotide is not locked into a helix in this structure and so the sequence can be described as I—I—BP—I—I—BP, emphasizing the propensity of platinum complexes for stacking interactions [61]. 

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Bailey JA, Miskowski VM, Gray HB. Spectroscopic and structural properties of binuclear platinum-terpyridine complexes. Inorg Chem 1993 32 369-370. 

Platinum(II) complexes containing the tridentate ligands diethylenetriamine (dien) and 2,2 6, 2"-terpyridine (terpy) have provided useful substrates for mechanistic studies in substitution reactions at planar four-coordinated complexes. Moreover, there has been considerable interest in terpy complexes... 

For example, in 1963 the photochemistry of magnesium phthalocyanine with coordinated uranium cations was studied in pyridine and ethanol and indicated the occurrence of PET to the uranium complex . A rapid photoinduced electron transfer (2-20 ps) followed by an ultrafast charge recombination was shown for various zinc and magnesium porphyrins linked to a platinum terpyridine acetylide complex . The results indicated the electronic interactions between the porphyrin subunit and the platinum complex, and underscored the potential of the linking para-phenylene bisacetylene bridge to mediate a rapid electron transfer over a long donor-acceptor distance. 

The metallointercalation reagents are a class of heavy metal derivatives that bind to double-stranded polynucleotides by inserting between adjacent base pairs in the helix.1 2 Prototype members of this class of intercalators are (2,2 6, 2"-terpyridine)(thiolato)platinum(II) complexes.3 These may be synthesized from chloro(2,2 6, 2"- terpyridine)platinum(II), which can both intercalate and bind covalently by losing chloride ion. Covalent binding of the thiolato complexes is much slower owing to the more inert character of the Pt—S bond. Metallointercalation reagents also have the potential to bind to proteins that have natural receptor sites for nucleic acid bases. They may therefore also be used to provide isomorphous heavy atom derivatives for X-ray analysis. 

Although there have been numerous reports of nickel(II), palladium(II), and platinum(II) complexes of 2,2 6, 2"-terpyridine, complexes in higher oxidation states are all but unknown. Morgan and Burstall described the... 

Figure 2.17 Solvatochromic ionic cr-alkynyl platinum(II) terpyridine complexes...

Many recents studies have focused on applications of metallointerca-lation, which is also an important noncovalent interaction of metal complexes with nucleic acids. Intercalation is a common mode of association of small molecules with DNA, where a flat aromatic heterocyclic moiety inserts and stacks in between the DNA base pairs (13). Lippard and coworkers (14) determined in 1974 that platinum(II) complexes containing an aromatic heterocyclic ligand such as terpyridine could intercalate in DNA. Figure 2c shows such a stacking interaction of such a complex in a dinucleotide (15). Recently, we have found that intercalation is not restricted to completely flat, square planar complexes, but partial intercalation of ligands coordinated to octahedral metal centers is feasible as well... 

Yam and co-workers reported the synthesis and characterisation of three platinum(n) terpyridine complexes [Pt( Bu3tpy)(C = C-C6H4-R-P)] (R = NH2, NCS, NHCOCH2I) (24) [62]. The isothiocyanate and iodoacetamide complexes show orange-yellow MLCT (dji(Pt) -> jt ( Bu3tpy))/ LLCT (jr (C = CR) ji ( Bu3tpy)) emission in various media. For example, in CH3CN... 

Michalec JF, Bejune SA, McMillin DR (2000) Multiple ligand-based emissions from a platinum(II) terpyridine complex attached to pyrene. Inorg Chem 39 2708-2709... 

Apart from the platinum(ii) diimine system, analogous platinum(ii) systems with planar tridentate ligands are also hot topics in current chemical research. Their useful physical and biological properties, such as interaction with DNA and proteins, were first reported by Lippard and coworkers [150, 151]. Subsequent reports by Che and coworkers described the luminescence properties of a series of platinum(ii) complexes with terpyridine ligands, [Pt(trpy)X] (X = Cl, Br, I, N3,... 

From the studies reviewed above it has become evident that competion studies between thiols/thioethers and intact double-helical DNA are required, to find out whether or not the formation of the Pt-GG chelate is a driving force that can overcome the Pt-S interactions. Even then, one should realize that we are only dealing with a model, as in the cell other metals might also play a role in the disruption of Pt-S bonds. In this respect it should be mentioned that it was recently reported that addition of transition metals such as Zn11 or Cu11 can cleave even the Pt-S bond in thiolated terpyridine-platinum complexes at neutral pH [87],... 

METALLOINTERCALATION REAGENTS THIOLATO COMPLEXES OF (2, 2 6, 2"-TERPYRIDINE)PLATINUM(II)... 

The synthesis of chloro(2,2 6, 2"-terpyridine)platinum(ll) was first reported by Morgan and Burstall in 1934.4 Better yields for this compound can be obtained by the method of Intille,s which is given below. The (2,2 6, 2"-terpyri-dine)thiolato compounds were reported in 1974,1 and a general synthetic procedure for these complexes was recently described.3 In this method silver ions are introduced during an intermediate step. Since silver is known to bind... 

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