M-N Bonds

Bent metal-NO bonding is traditionally associated with NO bonding as NO , whereas linear coordination is associated with NO+. The latter is predicted to involve shorter M-N bonds as both a- and 7r-donation can be involved. 

Comparative studies [1127] of the kinetics of decomposition of similar salts containing related pyridine ligands have been used to investigate the strength of M—N bonds in coordination compounds. Non-isothermal DSC measurements were used to determine values of E for the reactions... 

Activation energies were in the sequence py < 4-mepy < 3-mepy which is the order of M—N bond strengths. 

A similar approach, i.e., carbodiimide insertion into M-N bonds was used to prepare unusual zirconacarboranes containing guanidinate ligands. In an alternative approach, these compounds were also synthesized by the route outlined in Scheme... 

Transition metal alkyls are often relatively unstable earlier views had attributed this either to an inherently weak M—C bond and/or to the ready homolysis of this bond to produce free radicals. Furthermore, the presence of stabilizing ir-acceptor ligands such as Cp , CO, or RjP was regarded as almost obligatory. However, (1) the M—C bond is not particularly weak compared say to the M—N bond, and (2) the presence of the new type of ligand on the metal could make the complex kinetically stable thus, even isoleptic complexes, i.e., compounds of the form MR , might be accessible 78, 239). These predictions have largely been borne out (see Table VII). 

Based on the fact that pi-acids interact with the trinuclear gold] I) pi-bases, TR(carb) and TR(bzim), the trinuclear 3,5-diphenylpyrazolate silver(I) complex was reacted with each. Mixing [Au3(carb)3] or [Au3(bzim)3] with [Ag3(p,-3,5-Ph2pz)3] in CH2CI2 in stoichiometric ratios of 1 2 and 2 1 produced the mixed metal/mixed ligand complexes in the same gold-silver ratios. The crystalline products were not the expected acid-base adducts. It is suspected that the lability of the M-N bond (M=Au, Ag) in these complexes results in the subsequent cleavage of the cyclic complexes to produce the products statistically expected from the stoichiometry of materials used [74]. As a result of the lability of Au-N and Ag-N bonds, and the stability of... 

The reaction mechanism clearly involves the oxidative addition of aniline to an unsaturated Ir(I) complex (Scheme 4-4). Interestingly, the azametallacyclobutane intermediate could be characterized by single-crystal X-ray diffraction [141]. This result confirms that insertion of an olefin into the M-H bond is less favorable than insertion into the M-N bond [142]. 

Hg2+ complexes readily with DNA. Only one type of complex is formed independent of the base ratio and up to an r value of 0.5. Two protons are released at pH 5—7 per metal bound. There is no satisfactory model for this binding. The removal of the Hg2+by chloride reverses the changes in DNA in marked contrast with the irreversible changes induced by CHsHg+. It may be that it is a special feature of a metal which can form two N—M—N bonds reversibly in DNA. 

Figure 4. The Correlation between the M-N bond length (x-Axis) and the Si-N and Si-O bond lengths (y-Axis) in [Me2(tBuO)Si]->N)2M, M = Zn, Fe, Mn, Ca, Ba.

The more the cation becomes larger, the more the M-0 and M-N distances become closer together. This means that with small cations the M-N bond is dominant while with larger cations the oxygen atoms seem to take over the bonding at the expense of the M-N bond. This should of course have a direct impact on the bonding of the nitrogen to silicon. 

X-ray diffraction studies of the Co(n) and Co(m) sepulchrate complexes indicate that they have similar structures although, as expected, the M-N bond lengths are shorter (1.99 A) in the Co(m) complex than in the Co(ii) species (2.16 A). The Co(n) complex was obtained by direct reduction of the Co(m) analogue using zinc dust. A striking feature of the syntheses of these species is that the reactions proceed with retention of the configuration of the [Co(l,2-diaminoethane)3]3+ starting complex. 

Phosphorus, Arsenic, and Silicon and Germanium Porphyrins M—N Bond Length and Degree of Ruffling"... 

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