Monodentate ligands definition

With these definitions, it is possible to classify all monodentate ligands into one of the following five types ... 

Definition The ring chemical shift is dehned as the valne observed for the metallacycle compared to the chemical shift fonnd for a complex where the chelate ligand is replaced by two eqnivalent monodentate ligands. 

Attention should be paid to the fact that the ratio of Pd and phosphine ligand in active catalysts is crucial for determining the reaction paths. It is believed that dba is displaced completely with phosphines when Pd2(dba)3 is mixed with phosphines in solution. However the displacement is not eom-plcte[16]. Also, it should be considered that dba itself is a monodentate alkene ligand, and it may inhibit the coordination of a sterically hindered olefinic bond in substrates. In such a case, no reaction takes place, and it is recommended to prepare Pd(0) catalysts by the reaction of Pd(OAc)2 with a definite amount of phosphinesflO]. In this way a coordinatively unsaturated Pd(0) catalyst can be generated. Preparation of Pd3(tbaa)3 tbaa == tribenzylidene-acetylacetone) was reported[17], but the complex actually obtained was Pd(dba)2[l8],... 

All ligands can also be broadly classified as monodentate or as chelate depending on whether the ligand occupies one or more coordination sites of a single metal atom. A chelating ligand by definition is polydentate and is called bi-, tri-, or tetradentate depending on the number of coordination sites it occupies. 

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