Dipyridine ligands

Figure 9 Formation of giant vesicles by fusion of LUVs equipped with an amphiphilic dipyridine ligand and filled with rhodamine sulfonate (50 xM) in presence of NiCL (0.1 xM) observed by fluorescence microscopy. The time between the first panel (upper left) and the last one (lower right) was 7 s. Scale bar 10 pm. (Reproduced with permission from Ref. 61. National Academy of Sciences, 2004.)...

A related molybdenum-based allylation protocol was recently utilized by Trost in a concise total synthesis of the HIV protease inhibitor tipranavir (119, Scheme 14.19) [104], With dipyridine ligand 117, allylated product 118 was readily obtained with excellent yield and enantioselectivity (94%, 96% ee). 

Since 1980 the interest in this reaction increased because enantiospecificity was introduced and much more valuable products could be made. A wide variety of ligands was tested, such as chiral dipyridines, phenanthrolines, diphosphines, aminoalcohols, bis-oxazolines, bis-oxazolines with a third donor atom in the centre, bis-thioureas, diamines, etc [33], In 1981 the highest e.e. reported was still only 20%. For many years the best results were obtained with chiral diimines and phenanthrolines but e.e. s were below 70% [34], Pfaltz introduced bis-oxazolines for this reaction and obtained e.e. s as high as 91% [35] in 1991. 

Among several dipyridine derivatives developed as chiral ligands, a Rh catalyst with phenanthroline 13b having a pinane skeleton gave 4 with 76% ee in the reduction of 1, which was higher than that obtained with Rh-phenanthroline-oxazoline 13a [20], whereas the tetraden-tate dipyridine-bis(oxazoline) Bipymox 14 in combination with RhCl, gave 4 with 90% ee (S) [21]. 

An analogous system involved the condensation of pentane-2,4-dione (127) with 6,6 -6w(jV-methylhydrazino)-2,2 -dipyridine (126) in the presence of nickel(II) to generate the thirteen-membered complex 128. Treatment of the complex with sodium cyanide does not release the ligand, nor does the complex form when copper is used as the metal template U0). 

This class of macrocycles has recently been expanded to include the 2,2 -dipyridine subunit within the macrocyclic framework. Vogtle et al. have synthesized 175 (59%) and 176 (24%). Thus far, no complexes of these two ligands have been reported 119). 

Vogtle has also reported the synthesis of an analogous system (191 and 192) which possess a dipyridine bridging unit. The only complexes of ligand 191 reported thus far are of NaSCN, LiC104, and NaC104141>. 

Bipyridines (1UPAC), also known as bipyridyls, dipyridyls, and dipyridines, are aromatic nitrogen heterocycles that form complexes with most transition metals.1-5 This class of compounds contains six possible regioisomers—2,2 (1), 2,3 (2), 2,4 (3), 3,3 (4), 3,4 (5), and 4,4 (6)—most common of which is the bidentate chelate, (1), (bpy = 2,2 -bipyridine). Bipyridine ligands interact... 

Tetrazine derivatives have been used widely in making pyridazines by inverse electron-demand Diels-Alder reactions with dienophiles (see Scheme 10), followed by loss of nitrogen from the usually unstable intermediate if the dienophile has a triple bond or potential triple bond properties, the final pyridazines will be aromatic. From the coordination chemistry point of view 3,6-dipyridin-2 -yl-l,2,4,5-tetrazine and dimethyl 1,2,4,5-tetrazinedicarboxylate and their analogs are probably the most useful starting compounds for making relevant ligands. 

Azido complexes are coordination compounds with azide ions as inner-sphere ligands and may be cationic, such as azidopentaaquocobalt(III) (d) or anionic, such as hexaazidocuprate (e) or neutral, such as dipyridine diazidozinc (0- There are mixed-ligand complexes, such as (d) and (f), and all-azido... 

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