N acceptor properties

Substituted cyclopentadienyl with the pentamethyl group results in (i) increased covalent character of the metal-cyclopentadienyl bond, (ii) strong n donor and weak n acceptor properties, (iii) kinetic stabilization due to steric shielding of the metal ion, and (iv) increased thermal stability of the metal complexes, (v) decrease in tendency to form polymeric structures due to increase in intermolecular interactions, (vi) increased solubility in organic solvents, and (vii) increase in vapour pressure. 

NHC are strong a-donor ligands and are even more electron-rich than the already electron-rich trialkylphosphines. Whereas in the early 1990s n-acceptor properties of NHC were disputed, it became obvious that NHC can act as n-acceptors and that the degree of n-acccptance depends on the nature of the metal bound and the NHC itself (Sanderson et al. 2006). 

In contrast to alkyne ligands, alkenes are observed to bond side-on to one metal center in a cluster complex. This may reflect the poorer n-acceptor properties of an alkene compared to an alkyne. In all cases reported for single alkene units the ligand has been coordinated to a metal atom in a trinuclear cluster unit, and in the majority of cases the... 

Such a bond is realized with polymer ligands containing basic groups with o-dcmor and n-acceptor properties like pyridine, imidazole. Coordination chemistry is nearly equal to low molecular mdal ligands. 

If the substituting ligands have n acceptor properties, more than two carbonyl ligands can be replaced in simple thermal processes. We demonstrated that treatment of complexes 78 with trimethylphosphite at room temperature affords the trisphosphite-substituted complexes 85 105). When M equals Mo and W the remaining carbonyl ligand may be replaced by heating in neat trimethylphosphite [Eq. (70)]. The phosphite ligands in... 

The n acceptor properties of the cyclobis (paraquat-p-phenylene) manifest in the complexation and sensing of n donors such as hydroquinones [190]. The sensing properties of the cyclobis (paraquat-p-phenylene)-modified surface towards hydro-quinone are shown in Figure 20.15. It should be noted that the sensitivity for hydroquinone sensing could be tuned, based on the number of layers of the... 

When the platinum nucleophilicity scale was first proposed it was implied that one np, scale was applicable to all substrates and that plots of logk2 against npt°(Y) were linear, taking the form log 10 2 = S np, (Y) + C, where S is termed the nucleophilic discrimination factor of the substrate and C its intrinsic reactivity. Discussions of mechanism based on a comparison of nucleophilic discrimination factors are frequently encountered. Nucleophiles that do not retain their positions in the nucleophilicity scale, e.g. NO2", SeCN and SC(NH2)2, were termed biphilic by Cattahni since their behaviour could be explained by their n-acceptor properties. When the Pt reaction centre had a greater n-basicity than the standard complex (for example a smaller effective nuclear charge) the substrate was more reactive than predicted and vice versa. This concept had been deduced some years earlier by Bosnich from his work with octahedral Ru complexes... 

Calculations indicate that the planar s-trans conformation is 20-28 kJ mol more stable than the s-cis form owing mainly to the interaction of the lone pairs." Furthermore, it appears that the n-acceptor properties of the N=C—C=N skeleton increase in the sequence 2,2 -bipyridine < 2-pyridinecarbaldehyde-JV-methylimine < R-DAB." ... 

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