Axial donor ligand

Similar behaviour is found in many other carboxylates of Cu as well as their adducts in which axial water is replaced by other O-or A -donor ligands. In spite of a continuous flow of work on these compounds there is still no general agreement as to the actual mechanism of the interaction nor on possible correlations of its magnitude with relevant... 

N-heterocycles are a class of neutral ligands with strong coordination affinity to many metal ions. Since a number of neutral N-donors ligands are available, a wide range of oxo-centered triruthenium complexes with various N-heterocyclic ligands have been prepared through axial ligand substitution. By judicious selection of the N-heterocyclic type and modification of the substituents with different electronic and steric effects, the electronic, redox, and spectroscopic properties in these oxo-centered triruthenium derivatives are controllable. 

Scheme 12 Concept of hemilabile axial donor a-diimine ligand...

Fig. 5. Ten types of different structures identified by X-ray diffraction, where the abbreviated N-0 is used to express each bridging amidate ligand and X denotes axial donors such as OH2, N03, N02 (nitro), Cl, and Br. For the compounds involving axial ligands (X), the total complex charge is given assuming that X is a monoanion. Note that, in some cases, amine ligand in cis-Pt(NH3)2 will be replaced with other ligands, such as in Pt(en), cis-Pt(NH3)Cl, cis-PtCl2, and Pt(bpy).

When the water ligand of 5b is replaced by propenol as axial donor or in case of equatorial coordination of propenol at the metal center, intermediates are formed which could undergo intramolecular epoxidation through TSs S-6 and S-7b, respectively (Figure 11). Here, the prefix S indicates a transition... 

Fig. 4. The enviromnent of the di heme in various states of the P. pantotrophus cytochrome cdi. (a) The oxidized enz3rme. (b) The reduced enzyme, (c) The reduced enzyme to which nitrite has been added, (d) The reduced enzyme that has converted bound nitrite to nitric oxide. T3rr25 provides an axial oxygen ligand to the di heme iron in the oxidized enz3rme (a). This T3rr25 is displaced in the reduced enzyme (b) but can be seen returning to the di heme in the structures with nitrite (c) or nitric oxide (d) bound. His 345 and His 388 are proposed proton donors to the substrate. In (b) the di heme iron is five-coordinate. The water molecule (Wat) that is seen above the heme ring is not coordinated to the iron. Dashed lines represent potential hydrogen bonds. (Drawn from PDB entries 1 qks, 1 aof, 1 aom and 1 aoq.)...

It has been suggested that bis(equatorial) (ee) coordination of bidentate P-donor ligands in [HRh(CO)2(diphosphine)] (structure 5) can favor high linear/branched product ratios relative to systems which prefer equatorial-axial (ea) chelation (structure 6). For the bulky bis-phosphite 7 shown in Scheme 3.4, HP IR in conjunction... 

It has been suggested previously (Section 37.3.1) that the relatively short WVI—OR bond length is indicative of bond order greater than one. If this holds true for the Wv—OR bonds, then for complexes of the type [WX4(OR)2] the Jt donor ligands OR- will prefer trans stereochemistry since the d electron can be accommodated in the dxy atomic orbital vhich is orthogonal to the orbitals involved in the bonding of the n donor atom. Indeed, ESR spectra of the dialkoxo complexes are consistent with axial symmetry.160 This idea has also been put forth to explain the preference of the dioxo complexes with the dz electronic configuration for the trans stereochemistry. 

ESR spectroscopy has been used to examine molybdenum(III) complexes with Cl, O, S and N donor ligands.38 At temperatures between 5 and 80 K, these compounds show broad axial or rhombic signals centred at g = 2 and 4. For [Mo(acac)3] the estimated A values are 10 1 (x, y) and 12.2 0.5 (z) mK. Complexes with sulfur atoms which are part of an extended n system have typical ESR spectra, with all g values near 2. 

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