Phenanthroline, monodentate

Another rare example of monodentate phenanthroline is provided by PtCl(PEt3)2(phen) the non-bonding Pt-N distance is 2.843 A (Figure 3.34). 

Figure 3.34 The structure of PtCl(PEt3)2(phen) showing the monodentate phenanthroline...

Complexes of bulky substituted phenanthrolines [Pt(N-N)LX2] (L, X both monodentate N-N, e.g. 2,9-dimethyl- 1,10-phenanthroline) can be 5-coordinate tbp when a good 7r-acceptor (e.g. C2H4) is present or 4-coordinate with monodentate phenanthrolines. Hartree-Fock calculations indicate that the 7r-acceptors reduce the electron density at platinum so that the metal can accept charge from another donor. Species of this kind may be involved in alkene hydrogenation [138]. 

They form adducts with Lewis bases in which the phenanthroline is monodentate, PtX2(dimphen)L (L = Me2S, Me2SO, PhNO) [87], c/s-Pt(bipy)Cl2 exists in yellow and red forms, the difference in colour results from different stacking modes in the solid state, with respective Pt-Pt distances of 4.435 and 3.45 A [88]. 

Analogous to the dithiophosphate complexes, cis octahedral complexes are formed with bident-ate ligands like phenanthroline, 2,2 -bipyridine, or tmeda and trans octahedral complexes are formed with monodentate ligands like pyridine and its derivatives. Some examples are mentioned with linear bidentate ligands like 4,4 -bipyridine, which build up ID chains by bridging the [NiL2] molecules.926-933... 

They form adducts with Lewis bases in which the phenanthroline is monodentate, PtX2(dimphen)L (L = Me2S, Me2SO, PhNO) [87],... 

Numerous other aromatic nitrogen compounds are known, and a significant number have been used to prepare complexes of platinum(II). Phthalazine (101) is one such compound, and the complex ds-PtCl(phthalazine)(PEt3)2 has been prepared in order to compare its fluxional properties with the phenanthroline and naphthyridine analogues. The monodentate complex is fluxional, but in this phthalazine case the orientation of the lone pairs is unsuitable for the five-coordinate intermediate required by an intramolecular process and the mechanism of exchange becomes dissociative.11 6... 

In Table 1, the diimine ligands were either 2,2/-bipyridine or 1,10-phenanthroline, or one of their derivatives, although 2,2,-bipyrazinc and derivatives of 2,2 -bipyrimidine are also listed. Some monodentate chelating ligands contained one or more pyridine functionality and could bind an... 

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