Metals nitrogen donor ligands

Organometallic compounds apart, oxidation states below - -2 are best represented by complexes with tris-bidentate nitrogen-donor ligands such as 2,2 -bipyridyl. Reduction by LiAlH4 in thf yields tris(bipyridyl) complexes in which the formal oxidation state of vanadium is -1-2 to —1. Magnetic moments are compatible with low-spin configurations of the metal but. 

Formally, in each of these cases the disproportionation produces a positive metal ion and a metal ion in a negative oxidation state. The carbonyl ligands will be bound to the softer metal species, the anion the nitrogen donor ligands (hard Lewis bases) will be bound to the harder metal species, the cation. These disproportionation reactions are quite useful in the preparation of a variety of carbonylate complexes. For example, the [Ni2(CO)6]2 ion can be prepared by the reaction... 

High-Nuclearity Paramagnetic 3d- Metal Complexes with Oxygen- and Nitrogen-Donor Ligands Richard E. P. Winpenny... 

Although a wide variety of nitrogen donor ligands exist in transition-metal complexes, relatively few general types have been employed in those complexes that have been found to activate dioxygen. Generally, the ligands are at least bidentate, and often are multidentate. 

Niobium and tantalum halides form adducts with various nitrogen donor ligands including aliphatic and aromatic amines nitriles, Schiffs bases and imidazoles (Table 5). The reactions of MXS with pyridine and related ligands such as bipy or phen depend critically on the reaction conditions. With py at low temperature MX5 (X = Cl, Br) yielded 1 1 adducts that are rapidly reduced to [MX4(py)2] on increasing the temperature, with formation of l-(4-pyridyl)pyridinium halide. Similarly, bipy and phen reduced the metal in MeCN to oxidation state +IV and formed monoadducts of type [MX bipy)] at room temperature, while at 0°C the same reactions yielded [NbCls(bipy)(MeCN)] and [TaX5(bipy)(MeCN)J (X = C1 or Br). NbBrs and Tals formed [MX5(bipy)2], which were formulated as the eight-coordinate [MX4(bipy)2]X.1 Reduction of the metal can however be prevented, even at room temperature,... 

The nitrogen atoms in these iminoalkyl groups have pronounced nucleophilic character and can act as nitrogen donor ligands towards a series of metal atoms forming complexes of type 90 [M = Fe, Co, Ni, Cu, Zn ... 

The pentadentate nitrogen donor ligand 6.30 has a hole size of about 0.7 A and we predict that we could use a first-row transition metal ion as the template for its synthesis. The macrocycle is best prepared by the condensation of 6.31 with glyoxal about a nickel(n) template. In this condensation, most other metal ions are ineffective as templates. 

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