Macrocyclic ligands phosphorus

Numerous metal complexes have been proven to be active electrocatalysts for C02 reduction.1,66-68 These catalysts can be conveniently grouped into three main families metal complexes with polypyridyl ligands, metal complexes with macrocyclic ligands, and metal complexes with phosphorus ligands. 

Based on donor atom type, macrocyclic ligands can be considered to span two extreme types. First there are those systems which chiefly contain nitrogen, sulfur, phosphorus, and/or arsenic donors. These macrocycles tend to have considerable affinity for transition and other heavy metal ions they usually show much less tendency to form stable complexes with ions of the alkali and alkaline earth metals. The present discussion will be restricted to a consideration of a selection of such ligands and their complexes. 

Like their phosphorus(III) analogues, cycloarsoxanes (RAsO) undergo metal-mediated ring expansion to produce flexible macrocyclic ligands n = 5, 6, 8) that... 

Virtually all types of metal ions have been complexed with macrocyclic ligands.2-7 Complexes of transition metal ions have been studied extensively with tetraaza macrocycles (Chapter 21.2). Porphyrin and porphyrin-related complexes are of course notoriously present in biological systems and have been receiving considerable investigative attention (Chapter 22).8 Macrocyclic ligands derived from the Schiffbase and template-assisted condensation reactions of Curtis and Busch also figure prominantly with transition metal ions.6,7 The chemistry of these ions has been more recently expanded into the realm of polyaza, polynucleating and polycyclic systems.9 Transition metal complexes with thioether and phosphorus donor macrocycles are also known.2... 

The reaction of the palladium complex with diacetyl is rather more interesting and yields the palladium(n) complex of a novel tetraphospha macrocyclic ligand. Note that the phosphorus analogue of an aminol rather than an imine is once again obtained, representing the general instability of P=C bonds in the absence of sterically hindering substituents (Fig. 5-52). 

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