Transition metal effects

Interestingly, that the reactions of peroxynitrite with phenols were accelerated in the presence of ferric and cupric ions [112,114]. Until now, there seems no explanation of transition metal effects in these reactions. We just wonder if it is possible that ferric and cupric ions are able to oxidize peroxynitrite ... 

SCHEME 4. Transition metal effects on carbene chemistry. 

Some Facts Relevant to the Transition Metal Effect on Inhibiting Al Corrosion... 

The Post Transition Metal Effect, Lanthanoid Contraction and... 

If one compares the E(III)/E(V) (E = P, As) bond energies and the ionization energies of oxidation state -f-III P and As compounds, both the diminished stability of the As(V)-element bond [vs P(V)-element] and the unusual high Ip of As(III) compounds [vs P(III) compounds] can best be explained by the post transition metal effect (see above). Two examples from inorganic chemistry (just due to the better accessibility of data) are given in Table 2 . ... 

PMcs and AsMcj are essentially identical in their coordination behaviour towards the Lewis acid Ni (AsMej is the slightly better base). Although AsMcj and PMcj do not differ in their absolute electronegativities (post-transition metal effect, see above), AsMe3 is slightly softer than PMe3 which favours the coordination to Ni. An extensive discussion of the extended HSAB principle is given in the literature . ... 

Bi complexes are summarized in Table 5. The lack of As(V) complexes of the type R3 AsL2 may be explained by the resistance of As to realize high coordination numbers and oxidation states, which are usually discussed on the basis of the post-transition metal effect. Element(V) species of the type R3EL possessing only one carboxylato chelate ligand which coordinates symmetrically show trigonal bipyramidal structures. 

It was also proposed that the significant s and p orbital contraction at row four (Cu) is caused by the post-transition metal effect (d contraction), caused by an increase of the effective nuclear charge for the 4s electrons due to filling the first d shell (3d). A similar interpretation is possible for the row six (Au). This effect is commonly called lanthanoid contraction due to the effect of filling the 4f shell. The traditional explanation for the smaller size of gold (compared to Ag) is the lanthanoid contraction. However, this effect is only sufficient to cancel the shell-structure expansion, to make Au (nonrelativistic) similar to Ag (nonrelativistic). 

Metallodisilanes LnM-SiX2-SiX3 (X = H, Cl) represent interesting model compounds for the study of the transition metal effect , because these species contain both a transition metal substituted- as well as a metal-ffee Si-X unit in the same molecule. EtsN-assisted hydrolysis of the ferrio-pentachlorodisilane Cp(OC)2Fe-Si2Cl5 yields exclusively the ferriodichloro-trihydroxy-disilane 10, demonstrating the reduced susceptibility to nucleophilic attack at the silicon in the a-position to the transition metal atom. ... 

Keywords Transition Metal Effect / Metallodisilanes / Hydrolysis / Metallodisilanols / Metallosiioxanes... 

The transition metal effect , i.e. the stabilizing effect of the metal fragment on silanol units, can be raised considerably by attaching two transition metal fragments to the same silicon atom. 

An impressive example for the demonstration of the transition metal effect on the reactivity of SiH-units with respect to oxygen insertion is given by the bis(ferrio)-siloxane 9a, containing a metal-substituted as well as a metal-firee silicon atom. Due to the influence of the neighboring transition metal fragments the a-silicon differs considerably both in chemical and spectroscopic properties from the normal y-silicon. As a consequence, the reaction with dimethyldioxirane leads to the exclusive formation of the bis(ferrio)-disiloxanol 11, isolated in excellent yield (Eq. 2) [12]. The y-SiH moiety remains unaffected even when an excess of dimethyldioxirane is employed. 

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