Naphthyridine Complexes

As mentioned earlier, 1,8-naphthyridine and its derivatives are admirably suited to the preparation of metallic or other complexes. Although the details of such complexes are beyond the scope of this book, selected papers in this area are listed here according to the element or other entity involved. 

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The JHNMR spectrum of the platinum 1,8-naphthyridine complex (124) shows the naphthyridine protons to be equivalent above -30 °C, suggesting fluxional behavior (77IC261). Other examples of this phenomenon have also been observed (73JA4855). 

The platinum 1,8-naphthyridine complex (160) in the solid state shows square-planar coordination about platinum with the naphthyridine behaving essentially as a monodentate heterocycle.109... 

Naphthyridine will form complexes of the type ML2 with Cu(II), Co(II) and Ni(II) but not with Cd(II), Pd(II), Ba(II) or Zn(II) (66MI21101). 1,5-Naphthyridine 1,5-dioxide forms coordination compounds with Cu(II) salts (76IC2916), and metal complexes of l,7-naphthyridin-8-ones with Cu(II), Ni(II), Fe(II) and Fe(III) have also been prepared (54JCS505). A more detailed account of metal ion-naphthyridine complex formation is given in a recent review (83AHC(33)147). 

As for ten coordination, there are no twelve-coordinate complexes containing only unidentate ligands. The most common twelve-coordinate molecules are of the type [M(bidentate)6]. Three structural isomers may be formed by wrapping six bidentate ligands along the edges of an icosahedron (Figme 17). Isomer III is less stable than the other two and is not observed. Isomer I is observed for a number of hexanitrato complexes, for example [La(N03)6] and [Th(N03)6] . Isomer II has been observed for the naphthyridine complex [Pr(napy)6] +. 

The quantum yields for emission lines of these complexes are expected to increase as the coordination number about the rare earth becomes larger and as the energies of the ligand triplet state and ion resonance level approach one another. On the basis of these criteria, the naphthyridine complexes of Sm, Eu, Tb, and Dy might be expected to yield more intense emission spectra than similar phen and bipy complexes. Also, the number and splitting of emission lines observed for the europium complexes are indicative of the symmetry about the metal (9, 11, 15), and thus they may be used to delineate possible coordination geometries. For these reasons, we undertook an investigation of the fluorescence spectra of several naphthyridine complexes of Sm, Eu , Tb" and Dy" ... 

The compounds 87a and 87b are aminated at position 4, yielding the 4-amino compound (88a, 40%) and the 2,4-diamino compound (88b, 11%) respectively the 2-ethoxy compound (87c), however, undergoes amination at position 4 as well at position 5, giving a mixture of the 4-amino compound (88c, 20%) and the 5-amino compound (89a, 14%).Tlie 2-chloro compound (87d) yields a highly complex reaction mixture from which the 5-amino compound (89b), the 2,4-diamino derivative (88b), and 2,5-diamino-l,8-naphthyridine (89c) could be isolated. l-Ethyl-3-nitro-l,8-naphthyridin-2(lH)-one (90a) and 3,6-dinitro-l-ethyl-l,8-naphthyridin-2(lH)-one (90b) were aminated exclusively in the 4-position to give compounds 91a (62%) and 91b (45%), respectively (93LA471). 

Naphthylamine, 1-phcnylazo-metal complexes structure, 6,44 1,8-Naphthyridine metal complexes, 2, 92, 93 Neel temperature, 1, 258 Neocupferron... 

As already mentioned, Lippard and co-workers have also studied the -hydroxy dizinc unit found in metallohydrolases in a model system [Zn2L(/x-OI I)(/x-02PPh2)]2+, L = 2,7-bis [2-(2-pyridylethyl)-aminomethyl]-l,8-naphthyridine) 454 Hydrolysis of phosphodiesters and beta-lactams was studied and related to the PI nuclease and beta-lactamase enzymes. The dinuclear complex... 

In another avenue of research, in 1983, Ford and coworkers73 published work on a Rh(n) complex of 2,7-bis(2/-pyridyl)-l,8-naphthyridine (bpnp), referred to as [(bpnp)Rh2(02CCH3)3]PF6. The catalyst, and related species (.e.g., 2(2 -pyridyl)-1,8-napthyridine or pynp), displayed moderate activity in neutral, acidic, or basic mixed organic solvent/water solutions, as shown in Table 4. 

Diethyl 7V-ethyl-A-[6-(4-ethoxycarbonyl-l-piperazinyl)-5-fluoro-2-pyri-dyl]aminomethylenemalonate (1027) was cyclized on the action of boron trifluoride etherate complex in diphenyl ether at 228-231 °C for 30 min to give the 1,8-naphthyridine derivative (1028) in 90% yield [84JAP(K)80683]. 

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