OORDINATION COMPLEXES

Lever s model has been typically applied only to six[Pg.3753]

As mentioned above, the A term of the rate law shown in Eq. 13.10 could also arise from dissociation (D) of X to give a thiee[Pg.542]

Sketch a reaction profile for subsiiiution in a square planar complex in whkh (a) a five coordinate intennediate exists, but bond breaking is more important than bond making (b) a five oordinate intermediale exists, but bond making is more importanl than bond... 

More accurate force constants for a number of transition metal complexes with amine ligands have been derived by normalinfrared spectra [187, 188], The fundamental difference between spectroscopic and molecular mechanics force constants (see Section 3.4) leads to the expectation that some empirical adjustment of the force constants may be necessary, even when these force constants have been derived by full normal-coordinate analyses of the infrared data. This is even more important for force constants associated with bond-angle deformation (see below). It is unusual for bond-length deformation terms to be altered substantially from the spectroscopically derived values. 

In synthesis (b), the initial product is a 5hydride complex, which is rapidly oxidized in solution to the planar iridium(II) complex. Both of the compounds are paramagnetic with one unpaired electron, as expected for square planar d complexes. 

I. J. (1996) Dinitrogen cleavage by three[Pg.152]

In the solid state, there appear to be two common types of fiveSchifF bases. Green derivatives have v(V = O) close to 980 cm and yellow-brown derivatives have v(V = O) around 880 cm [89]. In solution, the A, A -2,2-dimethyltrimethylenebis[salicyli-deneiminate] (salnptn) ligand forms the complexes shown in Eig. 16 as expected, but it is orange in the solid state with very close axial V—0=V contacts and v(V=0) at 871 cm [89]. This complex... 

CIS-VO2 complexes with tridentate Schiff-base ligands also appear, and they sometimes have fivesquare-pyramidal structures with one oxo-ligand at the apex. Many of these species have reversible features in their CVs at = ca —0.07 V versus Ag/AgCl/MeOH and can undergo a photoreduction in the solid state which can be reversed by dissolution [110]. 

Manganese forms a large number of mononuclear complexes in oxidation states II, III, and IV with acychc and other common ligands. The complexes primarily are sixpseudo-octahedral geometries. Some exceptions to this categorization are the tetraoxo anions in oxidation states V, VI, and VII and the manganocenes. Table 1 contains electrochemical data for representative redox couples in which the Mn coordination environment remains invariant with oxidation state. Many entries are for homoleptic complexes, but some species with mixed... 

Thus, the reductive eliminations from tranx-bis(triphenylphosphine) amido-aryl complexes 86 showed first-order kinetics demonstrating that the reductive elimination takes place from monomeric species (Scheme 1.54). The dependence of the reaction rate on the concentration of added PPhj is compatible with two competing mechanisms, one involving C-N bond formation to a ds-16-electron species 87 formed by isomerization of the trans derivative. The other mechanism involves initial reversible phosphine dissociation to give a 14-electron threebond formation (Scheme 1.54). Dimeric monophosphine complexes follow a dissociative pathway to give threereductive elimination. The formation of the 14-electron intermediates can be reversible or irreversible depending on the type of amine. 

Consistent with these results, as shown in Fig. 7.33, the DFT calculations of the CH activation mechanism show that the lowest energy pathway involves pre-equilibrium, dissociative loss of pyridine to generate a trans-5rate-determining trans-cis isomerization to generate the cis-benzene complex and fast CH bond cleavage by a sigma-bond metathesis transition state. 

For the lactamolytic mechanism [14], a complexation of the cation with the growth center is assumed 27, whereas the ioncomplex between the growth center and the lactamate 28 ... 

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