A donor strength

The same group has also investigated alkyl and silyl acetylides, as opposed to the aryl acetylides of most of the other studies. The a-donor strength of the... 

Finally the reversal in the most favorable relative a donor strength of the two apical ligands on going from the pathway B to the pathway C may be related to a different nature of the transferred hydrogen The pathway B may be viewed as involving a transfer of a hydride, II , to a coordinatively unsaturated trigonal pyramid moiety acting as a Lewis acid. The pathway C, on the other hand may be viewed formally as an oxidative addition of on the coordinatively saturated square pyramidal d center. 

An analysis of the effects of substituents on the basicity of phosphines has been presented,and the relationship between phosphine-proton affinities and lone pair density properties explored. A scale of a-donor strengths for phosphines and related systems has been developed. The model supports the view that as a-donor strength increases, so the 7C-acceptor power declines. Theoretical approaches to the electronic structures of phosphirane and 1,3-diphosphe-... 

The a value measures the intrinsic reactivity of the complex, and p measures how much the rate is affected by the a-donor strength of the ligand. The result is a Hammett-type linear free energy (LFE) relationship. 

The electronic structures of a range of compounds (acyclic, cyclic and heterocyclic) have been explored by DFT calculations. It was more specifically shown that the charge of the divalent carbon compound exhibit the main contribution to the tr basicity (related to the a donor strength) followed by the nature of the atom a to the divalent carbon. This effect has been shown to propagate along the chain. The nature of the n system is less related to the structural nature of the molecules but fits well with the description of the n molecular orbitals which explain both the n acidity and the n basicity. 

As seen for the octahedral splitting pattern in Figure 15.1, it is the highest occupied molecular orbital (HOMO), t2g, and the lowest unoccupied molecular orbital (LUMO), 2eg, which are the focus of our attention in the rest of this book. They are shown in 15.1 I. The energy gap between t2g and leg is a function of the ligand a donor strength... 

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