Cyanides ligands

A series of complexes in which the cyanide ligands are modified or replaced arises from the decomposition of methyl and pyridiomethylcobalt(111) pentacyanide derivatives in acid solution. The reactions include protonation of a cyanide ligand, insertion of a cyanide ligand between the organic group and the cobalt atom to produce an imine (see Section VI,D), decomposition of this imine to an acyl product, and replacement of a cyanide ligand by water 100, 101). The products are listed in Table III, 29. 

Reissmann S, E Hochleitner, H Wang, A Paschos, E Lottspeich, RS Glass, A Bock (2003) Taming of a poison biosynthesis of the NiFe-hydrogenase cyanide ligands. Science 299 1067-1070. 

The choice of isothiocyanate as the anionic ligand is to some extent historical, but it seems to be a very appropriate ligand with an intermediate ligand field strength. The variation in ligand field strengths for a list of cyanide ligands is ... 

Lyon, E. J., Georgakaki, I. R, Reibenspies, J. H. and Darensbourg, M. Y. (1999) Carbon monoxide and cyanide ligands in a classical organometallic complex model for Fe-only hydrogenase. Angew. Chem. Int. Ed. Engl., 38, 3178-80. 

All the alkenyl, -aryl, -acyl, -iminoacyl, -alkynyl, cyanide ligands (C(R)=E or C=E)... 

The removal of iron from such species as transferrin or ferritin by hydroxypyridinones, side-rophores, and other chelators is of considerable relevance to the control of iron levels in the body, and indeed to iron metabolism in a range of life forms. Methods and mechanisms for such removal are referenced in Sections 5.4.5.2,5.4.5.5.2, 5.4.5.6.1, and 5.4.5.6.2 below. Interestingly cyanide, one of the most powerful ligands for iron, appears to prefer to bind to iron-transferrin, at the C-terminal Fe, rather than to remove the iron. This adduct is believed to contain the iron in an octahedral environment of three cyanide ligands mer) and nitrogens from two tyrosine residues and a histidine. ... 

In the ternary complexes [Fe(127)(CN)2] the normally pentadentate macrocyclic aza-terimine ligand is only tetradentate, thanks to the particularly advantageous combined ligand field of two cyanide ligands and four nitrogen donor atoms in octahedral geometry. ... 

There are a number of osmium(VI) oxo complexes containing cyanide ligand, but none have been reported for ruthenium. The ion [0s(0)2(CN)4] can be prepared by reaction of [OSO4] with aqueous KCN. The X-ray crystal structure of Cs2[Os(0)2(CN)4] (85) shows that it has trans-6ioxo groups with 0s=0 distances of 1.750 [0s(0)2(CN)4] is luminescent both in the solid state... 

A similar effect conceivably accounts for the higher Pi value (—0.74 V) (weaker net electron-donation) of the cyanide ligand estimated [15] at trans- FeH(dppe)2 with the strong donor trans-hydride, in comparison with that (—l.OV) [10] obtained at Cr(CO)5 and also proposed at trans- MoL(dppe)2) (L = CO, N2) with the strong net electron-acceptor L ligand, in spite of the lower electron-richness of the former Fe site Eg = 1.04 V) relatively to the latter (Eg = —0.11 or —0.13 V) molybdenum centers. 

This formulation, which is kinetically indistinguishable from that given by Equation 5, would require that the numerical value of 0.31 be assigned to the quantity kzK/kz, where K is the association constant for 13 formation. Finally, it should be emphasized that nothing is known about the geometry of the activated complex generated by either Reaction 5 or 9. To be more specific, the I2 molecule may be bonded to I , to a cyanide ligand, or to the t2g electrons of the Co(III) ion. 

Similar acetylene addition reactions take place with bis-cydopentadienylnickel carbonyl dimer (93). Changing from carbonyl to cyanide ligands seems to allow the formation of a true vinyl derivative. Thus, potassium pentacyanocobaltate, which may react as a dimer with a cobalt-cobalt bond (20), reacts with acetylene to give the adduct XV (31). The product was thought to be the trans isomer, but the data were not conclusive. 

The one-electron reduction of NP is associated with an increase in the population of the antibonding FeNO orbital. Figure 6a shows the DFT computed LUMO of NP (58), and Fig. 6b shows the IR electrochemical response for the [OsII(CN)5NO]2 ion (59) upon one-electron reduction in acetonitrile. The spectral characterization of the osmium-nitrosyl reduced complex could be done successfully because of the inertness of the Os-L bonds (L = NO or cyanide). In contrast, NP rapidly releases a cyanide ligand upon reduction in acetonitrile (57b,57d). The strong decrease of both the vqn and v o stretching frequencies in [Osn(CN)5NO]3 is very noticeable, particularly uN(> This is as predicted from the LUMOs description, since the addition of electrons to [OsII(CN)5NO]2 must weaken the NO bond. 

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