6-Substituted 2,2 -bipyridines, platinum complexes

Extensive use of vicinal proton-proton couplings has been made by Fraenkel and Qiu in their studies on the structure and dynamic behaviour of several methyl substituted allylic lithium compounds, by Shestakova et who studied the structure of the complex between lanthanum(III) nitrate and 1,9 diaza-18-crown-6, and by Goto et whose subjects of interest have been square-planar ternary platinum(II) complexes with A -ethyl- or A -benzyl-1,2-ethanediamine and 2,2 -bipyridine or 1,10-phenanthroline. 

A wide-ranging study of several cyclometallated analogs of platinum(ii) terpyridine/chloro complexes has been undertaken.Crystal structures were determined, and substitution kinetics experiments in methanol were conducted. The nucleophiles Br and Gl were employed, and in two cases, [Pt(N-N-C)Cl] and [Pt(N-G-N)Gl], substitution kinetics with TU, DMTU, and TMTU were measured. N-N-CH is 6-phenyl-2,2 -bipyridine, N-CH-N is l,3-di(2-pyridyl)benzene, TU is thiourea, and DMTU and TMTU are the dimethyl and tetramethyl analogs of TU. The complexes are schematically represented below 5. 

Several other recent reviews contain material relevant to this section. An article by Blandamer and Burgess on the thermodynamics, kinetics, and mechanisms of solvation, solvolysis, and substitution in nonaqueous solvents contains a contribution on the controversial dissociative mechanism for isomerization of square-planar molecules. This is outlined in Section 5.5. A review of ligand substitution reactions at low-valency transition-metal centers contains sections on five-coordinate metal carbonyl complexes and on ML4 complexes (mainly tetrahedral configurations with L being a tertiary phosphine), as well as on acid- and base-catalyzed reactions. A review by Constable " surveying the reactions of nucleophiles with complexes of chelating heterocyclic imines contains a sizable section on square-planar palladium and platinum derivatives. Most discussion centers on [Pt(bipy)2] and [Pt(phen)2] (bipy = 2,2 -bipyridine phen = 1,10-phenanthroline). The metal center, ligand, or both are susceptible to nucleophilic attack and the mechanisms involved are critically assessed. 

---