Metal-nitrogen bond

Two types of NO coordination to ruthenium are known linear Ru-N—O 180° and bent, Ru-N-O 120°. Since NO+ is isoelectronic with CO, linear Ru-N-O bonding is generally treated as coordination of NO+, with bent coordination corresponding to NO- thus, in the former an electron has initially been donated from NO to Ru, as well as the donation of the lone pair, whereas in the latter an electron is donated from the ruthenium to NO (making it NO-) followed by donation of the lone pair from N. Though an oversimplification, this view allows a rationale of metal-nitrogen bond lengths, as with the Ru—NO+ model 7r-donation is important and a shorter Ru—NO bond is predicted - and, in fact, observed. 

One-electron oxidation of the vinylidene complex transforms it from an Fe=C axially symmetric Fe(ll) carbene to an Fe(lll) complex where the vinylidene carbon bridges between iron and a pyrrole nitrogen. Cobalt and nickel porphyrin carbene complexes adopt this latter structure, with the carbene fragment formally inserted into the metal-nitrogen bond. The difference between the two types of metalloporphyrin carbene, and the conversion of one type to the other by oxidation in the case of iron, has been considered in a theoretical study. The comparison is especially interesting for the iron(ll) and cobalt(lll) carbene complexes Fe(Por)CR2 and Co(Por)(CR2) which both contain metal centers yet adopt... 

Tables 15 and 16 show the absorption maxima of some metal complexes of benzothiazolyl-substituted formazans 230 and 231.283 The wavelengths are metal ion dependent, making formazans useful reagents for the identification of specific metal ions or the simultaneous determination of two ions. The wavelengths are much longer than those of the formazan anion (Table 14). The general trend for electron-rich substituents is toward a larger shift this is to be expected as it tends to enhance the aromatic character of the ring and increase the covalent character of the metal — nitrogen bond. The sharpness of the absorption band has been attributed to coordination to the heterocyclic nitrogen as in 232.57S...

Metal-Nitrogen Bond Lengths and Torsion Angles between the Metal and Nitrogen Coordination Planes for Three-Coordinate Aluminum, Gallium, Indium, and Thallium Amides... 

Insertion into metal nitrogen bonds is illustrated by the formation of the anion [(C6F5)2Pd(S2CNIIPh)] in the reaction of [Pd2(C6F5)4(p-NHPh)2]2-with carbon disulfide.362... 

Trends in metal-nitrogen bonding can be illustrated by series of nitrido (H3MN, M = W, Os) and imido (H3MNH, M = Ta, Re, Ir) complexes, isovalent counterparts... 

Finally it is noteworthy that information on metal-nitrogen bond strengths in group 12 metal amides originally described in the 1980 edition has since been published in the... 

Table 8.1 Metal-nitrogen bond lengths in isoleptic aluminium and gallium amides...

Adducts have also been obtained by the reaction of methylmagnesium iodide with 3,5-dicyanopyridine and related substrates.138 Their formation involves a shift in the IR spectrum from 1563-1575 cm 1 to 1612-1645 cm"1, for C=C bonds, and from 2230-2248 cm 1 to 2125-2225 cm for the C=N bond, the final values being near the absorbance of the dihydro derivatives. Hydrolysis yields the expected dihydro derivatives. In connection with the nature of metal-nitrogen bond, it is of interest that in the sodium adduct 94 the IR spectrum indicates appreciable electron delocalization relative to the corresponding dihydro derivative (shift toward lower frequency), which suggests a substantial ionic character of the bond due to the low electronegativity of sodium. 

The suggested literature mechanisms for the first step of the diimine ligand oxidation in basic solution include (1) simple electron transfer, (2) dissociation of a ligand proton, (3) adduct formation at a ligand carbon atom, and (4) dissociation of a metal-nitrogen bond. These four mechanistic possibilities are shown in Scheme 1 and are discussed below. 

Mechanism 4 requires substitution at the metal center with concomitant dissociation of a metal nitrogen bond as the first step. It is generally accepted that complete dissociation of a bidentate chelate ligand is a two-stage process, and that breaking of the second bond in stereo-... 

The mechanism depicted in Scheme 2 involves two main steps. Rupture of the first metal-nitrogen bond accompanied by coordination of a water ligand at the metal center is followed by reversible deprotonation and intramolecular reduction of the metal center. Under the experimental conditions wherein the concentration of base is much larger than the concentration of tris(diimine) complex, and, applying the steady-state approximation to the concentration of the intermediate species with the monodentate diimine ligand, Eq. (6) can be derived as... 

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