Platinum complexes supramolecular

After Breit and Seiche (67) had reported hydroformylation catalysts containing rhodium and bidentate ligands assembled via hydrogen bonding, Dubrovina and Boerner (68) pointed out that the first use of bidentate ligands obtained via hydrogen bonding in catalysis is represented by the supramolecular work on SPO platinum complexes. 

Heavy metals, especially the third row transition elements, are useful reagents in biology and biochemistry. The high electron density of these elements (notably tungsten, osmium, platiniim and gold) makes them well suited for revealing aspects of supramolecular structures in electron microscopic images (l). More recently, simple platinum complexes have become widely used in cancer chemotherapy ( ). 

Nickel and platinum complexes of alkynols and alkynediols are an interesting class of organometallic complex self-associated by O-H- -O hydrogen-bond interactions. Their solid-state supramolecular assembly has been the subject of thorough studies [127]. 

Bimetallic platinum complexes are known as unique building blocks and are widely utilized in the coordination-driven self-assembly of functionalized supramolecular metallacycles. A detailed photophysical study of some bimetallic platinum compounds (see formula below) has been carried out, evidencing the role of H bonding with the solvent. 

Supramolecular systems assembled by peripheral and axial coordination were also thoroughly described. For example, heteroarrays held by axial coordination, particularly of zinc, nickel, ruthenium, tin, silicon, etc. porphyrins and phthalo-cyanines to peripheral pyridyl and 4,4-bipyridyl groups were described. Another interesting class of compounds are porphyrin dimers prepared by coordinative assembly of cw- icso-(4-pyridyl)porphyrins with PdCla forming two [PtCl2(pyP)2] complexes, and more complex tesselated structures by substitution of the platinum complex chloro ligands by 2,3-diamine(azaporphyrins), as depicted in Fig. 12. 

While today the construction of such bidentate phosphine ligands with the use of an assembly metal is referred to as supramolecular chemistry, this is not to say that there are no examples in older literature utilizing this principle. Actually, there are many and using as a search term hetero bimetallic complexes (a named coined in the early 1980s) leads us to a plethora of complexes. For instance in complex 29, reported by Rauchfuss in 1982, one would consider copper as the assembly metal and platinum as the potential catalytic metal [70]. 

As far as we are aware, the number of luminescent extended systems with gold-platinum interactions is reduced to only one report. This is a puzzling situation since the situation of platinum in the periodic table suggests considerable relativistic effects for this atom and extended chains of squared-planar Pt(II) cation-anion complexes built by metal-metal interactions are not strange. In fact, salts such as [Pt(CNR)4][Pt(CN)4] ,67 which are luminescent and display vapochromic behavior, and the modified form of the Magnus salt [Pt(NH3)4][Pt(CN)4] ,68 which shows semiconducting properties, are examples of this type of supramolecular systems. Therefore, the stable combination of gold and platinum in cation/anion-acid/base systems should be anticipated. 

The simplest supramolecular bidentate ligand derives from secondary phosphine oxides (SPO). Complexes of transition metals with SPOs have been known for 45 years, and they were introduced as catalysts by van Leeuwen and Roobeek in the early 1980s (66). The complex used first was a platinum hydride containing two SPOs, cormected to one another by a strong hydrogen bond, and a triphenylphosphine to complete the coordination sphere. SPOs have a very strong tendency to occur in pairs connected by hydrogen bonds in many metal complexes they act as bidentate monoanions. 

Ikeda, M., Tanabe, Y, Hasegawa, T. et al. (2006) Construction of double-stranded metaUo-supramolecular polymers with a controlled helicity by combination of salt bridges and metal coordination. Journal of the American Chemical Society, 128,6806-6807 Furusho, Y., Tanabe, Y. and Yashima, E. (2006) Double helix-to-double helix transformation, using platinum(II) acetylide complexes as surrogate linkers. Organic Letters, 8, 2583-2586 Furusho, Y. and Yashima, E. (2007) Molecular design and synthesis of artificial double helices. Chemical Record, 7, 1-11. 

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