Cis ligands

The complementary roles of trans, entering, and leaving ligands when contrasted with the much smaller role of variable cis ligands suggest an explicit model for... 

Hydroxide attack on complexes of the type cis-[(NO)L(bpy)2Ru ] also yields the corresponding nitro complex [118]. The equilibrium constants for these reactions are a strong function of the cis-ligand and increased by 10 on changing L from a jr-donor (Cl ) to a rr-acceptor (py) [98]. The ability of the nitro complexes to transfer an oxygen atom to a reductant such as triphenyl-phosphine is also a function of the cis-ligand [98]. 

Three distinct structural types are available for a tetracoordinated fragment a square planar structure of symmetry, a nonplanar square pyramid with C4t> symmetry, a nonplanar structure with Cjv symmetry (which would result from the removal of two cis ligands from an octahedral MLg), and the tetrahedral structure of symmetry Td- These are shown in Figure 13.5 in the standard orientation. The orbitals of the Z>4/, structure... 

Figure B13.3. (a) Comparison of bonding of CO and ethylene to Pd(II). (b) Distortion of bound ethylene to favor interaction between tlqC and a cis ligand, (c) Compared to interaction with 0 of ligated CO or acyl group.

In contrast to the very strong dependence of reactivity on the electron displacement properties of the trans ligand, there is small response to such variations in the cis ligand. There are no obvious ground state effects (cis influences) and it must be concluded that the effect, such as it is, relates to transition state stabilization. This is borne out by the fact that the effect is more marked the... 

The interrelationships between activation of H2 and other a-bonded molecules such as alkanes and silanes are highly significant because catalytic conversion of methane and other alkanes is strongly being pursued (17-19). An important question thus is whether C-H bonds in alkanes, particularly CH4, can bind to superelectrophilic metal centers to form a a alkane complex that can be split heterolytically where proton transfer to a cis ligand (or anion) takes place followed by functionalization of the resultant methyl complex (Eq. (3)). 

A major question is whether heterolytic cleavage of the H3C-H bond occurs as depicted in Scheme 10 (maintaining the Ptn state) or whether oxidative addition to a PtIV methyl hydride complex takes place. In such systems transfer of protons would be expected to be very facile because of the extremely high mobility of H +, and even a short-lived, very weak a complex could be a key intermediate. The C-H bond is likely to be polarized towards Cs H5+ on such highly electrophilic cationic metal complexes, where H+ can very rapidly split off and transfer to either a cis ligand or the anion as soon as the... 

In this Nb6 cluster, each edge is involved in bonding with a pi-CI ligand, so the edges do not correspond to 2c-2e Nb-Nb bonds. Each face of the Nb6 cluster forms a 3c-2e NbNbNb bond, and has bond number 2. The sum of bond number, 16, is just equal to the bond valence of 16, as shown in the front and back views of the Nb cluster in Fig. 19.1.2(b). 

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