N 2 ligand

Zn — Zn in acid solution —0-76 volts) Apart from possible Zn and Zn2 in some melts all zinc compounds are in the +2 state, generally in octahedral or tetrahedral co-ordination. Readily forms complexes, particularly with O and N ligands. 

The S-donor ligands SO, S2O2 and SO2 are mentioned in Section 15.2.5 and S-N ligands in Section 15.2.7. Thiocyanate (SCN ) is ambidentate. but towards heavier metaLs it... 

First isolated from D. desulfuricans (28), desulfoferrodoxin (Dfe) was also isolated from D. vulgaris (29). D is a 28-kDa homodimer that contains two monomeric iron centers per protein. These iron centers were extensively characterized by UV/visible, EPR, resonance Raman, and Mossbauer spectroscopies (30). The data obtained were consistent with the presence of one Dx-like center (center I) and another monomeric iron center with higher coordination number (penta or hexacoordinate), with 0/N ligands and one or two cysteine residues (center II). Comparison of known Dfx sequences led to the conclusion that only five cysteines were conserved, and that only one of them could be a ligand of center II (31). 

Start with a database of randomly chosen N ligands of length M grown in the binding site of protein P. 

In addition to tri- [105] and tetradentate N-ligands, mononuclear and dinuclear iron complexes with pentadentate N,N,N,N,0-ligands were applied to alkane... 

In recent years, several model complexes have been synthesized and studied to understand the properties of these complexes, for example, the influence of S- or N-ligands or NO-releasing abilities [119]. It is not always easy to determine the electronic character of the NO-ligands in nitrosyliron complexes thus, forms of NO [120], neutral NO, or NO [121] have been postulated depending on each complex. Similarly, it is difficult to determine the oxidation state of Fe therefore, these complexes are categorized in the Enemark-Feltham notation [122], where the number of rf-electrons of Fe is indicated. In studies on the nitrosylation pathway of thiolate complexes, Liaw et al. could show that the nitrosylation of complexes [Fe(SR)4] (R = Ph, Et) led to the formation of air- and light-sensitive mono-nitrosyl complexes [Fe(NO)(SR)3] in which tetrathiolate iron(+3) complexes were reduced to Fe(+2) under formation of (SR)2. Further nitrosylation by NO yields the dinitrosyl complexes [(SR)2Fe(NO)2], while nitrosylation by NO forms the neutral complex [Fe(NO)2(SR)2] and subsequently Roussin s red ester [Fe2(p-SR)2(NO)4] under reductive elimination forming (SR)2. Thus, nitrosylation of biomimetic oxidized- and reduced-form rubredoxin was mimicked [121]. Lip-pard et al. showed that dinuclear Fe-clusters are susceptible to disassembly in the presence of NO [123]. 

Figure 2.3 Selected examples of (pentafluorophenyl)gold(lll) complexes with monodentate N-ligands.

Figure 3.4 Complexes obtained by reaction of [Au(C6F5)(tht)] with different N-ligands.

Carbene gold(III) with diamine ligand can coordinate a second metallic center, since the N -ligand contains a free N H 2 group and can react with a new gold isocyanide under the formation of double dinuclear carbenes [46] (32). 

Scheme 1.28 Test reaction with binaphthalene-templated S/N ligand with achiral oxazoline pendant.

These workers have developed another new type of chiral S/N ligands, namely aziridine sulfides, which were easily synthesised in a straightforward synthetic route from inexpensive and readily available (i )-cysteine. The efficiency of this sterically and electronically varied set of ligands was then examined as chiral catalysts in the palladium-catalysed test reaction. The alkylated product was obtained in excellent yields and stereoselectivities of up to 99% ee, as shown in Scheme 1.44. 

In 2000, other S/N-ferrocenyloxazolines were prepared by Ai t-Haddou et al. starting from ehiral 2-amino-3-phenyl-l,3-propanediol. The corresponding P/N-analogues were also prepared in order to compare their efficiency in the test reaction. As shown in Scheme 1.68, both ligands gave good results in terms of both activity and enantioselectivity with a better result for the S/N ligand. 

---