Iron hydride complexes structure

Fig. 1 The first X-ray crystal structures of three types of the iron hydride complexes...

The ort o-metalated iron hydride complexes [HFe(CO)2 P(OPh)3 (PhO)2POC6H4 ] with R C=CR (R =Ph, R2 = Mc R = R2 = Mc R =Me, R2 = CH(OEt)2 R =Me, R = CH20H R = R = CH20H) in the presence of hydrated zinc chloride give a series of ferracyclopentendione complexes 203 <2000JOM(612)61>. With phenylace-tylene under similar conditions, the ferrole-type species 204 is formed with structural parameters similar to those... 

Table III also shows the values of the equilibrium constants, KVAp for the conversion of iron nitrosyl complexes into the corresponding nitro derivatives. Keq decreases downwards, meaning that the conversions are obtained at a lower pH for the complexes at the top of the table. Thus, NP can be fully converted into the nitro complex only at pHs greater than 10. The NO+ N02 conversion, together with the release of N02 from the coordination sphere, are key features in some enzymatic reactions leading to oxidation of nitrogen hydrides to nitrite (14). The above conversion and release must occur under physiological conditions with the hydroxylaminoreductase enzyme (HAO), in which the substrate is seemingly oxidized through two electron paths involving HNO and NO+ as intermediates. Evidently, the mechanistic requirements are closely related to the structure of the heme sites in HAO (69). No direct evidence of bound nitrite intermediates has been reported, however, and this was also the case for the reductive nitrosylation processes associated with ferri-heme chemistry (Fig. 4) (25).

When triethanolamine H3L13 (35) was reacted with sodium hydride and iron(III) chloride, the hexanuclear centrosymmetric ferric wheel [Nac Fe6(L13)6 )Cl (36) was isolated. Amidst a set of possibilities in the template-mediated self-assembly of a supramolecular system, the one combination of building blocks is realized that leads to the best receptor for the substrate [112]. Therefore, the six-membered cyclic structure 36 is exclusively selected from all the possible iron triethoxyamine oligomers, when sodium ions are present. The iron(III) complex 36 is present as an Sg-symmetric wheel, with an encapsulated sodium ion in the center and a chloride counterion. Consequently, the trianion (L13)3- acts as a tripodal, tetradentate, tetratopic ligand, which each links three iron(III) ions and one sodium ion. In the presence of cations with different ionic radii, different structures are expected. Therefore, when triethanolamine H3L13 (35) was reacted with cesium carbonate and iron(III) chloride, the octanuclear centrosymmetric ferric wheel [Csc Fe8(L13)8 ]Cl (37) was isolated (Scheme 13) [113]. 

Only two reports deal with the reactions of cobalt complexes with HFA. Insertion into the cobalt-hydrogen bond of a hydride complex affords a cobalt hexafluoroisopropylate 136a). An oxolene(2) is formed from an alkylcobalt compound and HFA 66). For mechanistic reasons the authors favor the depicted structure 157 over the isomeric oxolene (3) ring reported for the analogous iron complex 149 174). 

Oxidative addition of transition metal-hydride and transition metal-carhon bonds to zero-valent transition metal complexes provides convenient method for preparation of homo- and heterodinuclear organometallic complexes. Oxidative addition of iron-hydride to zero-valent platinum complex giving Fe-Pt heterodinuclear complexes was demonstrated hy the reaction of HFe[Si(OMe)3](CO)3(/c -dppe) with zero-valent platinum complex such as Pt(C2H4)3 or Pt( 1,5-cod)2 giving eventually heterodinuclear ethyl or cyclooctenyl complex (Scheme 3.86) [175]. The resulting heterodinuclear structure is stahihzed hy the bridging dppe ligand and the siloxo moiety. 

Structural and acid-base studies on the diiron azadithiolato complexes show that the basicity of the amine is diminished versus EtjN in the same solvent [37, 42]. Theoretical calculations suggest that the reduced basicity is arises from an electronic interaction between the nitrogen lone pair and the C-S a orbital (Fig. 12.4). The conjugate acid of this weakly basic amine would be capable of protonating a weakly basic iron hydride to generate hydrogen. 

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