Z-Ligand

Over the last decade, significant progress has been made in this area, especially via the incorporation of Lewis acid moieties into multidentate, ambiphilic ligands.

The understanding of the nature and influence of metal→Z-ligand interactions has considerably improved and the scope of Lewis acids susceptible to behave as σ-acceptor ligands has been significantly extended.

Owing to the vacant orbital present in Z-ligands, many have incomplete octets which allow them to readily accept a pair of electrons from other atoms.

In addition to the simple Lewis acids, there are several complex molecules that can act as both L- and Z-ligands.

These are referred to donor buttresses, and are typically formed when large boron-alkyl molecules complex with a metal center.

On the right is a typical reaction of a Z-ligand where the electron deficit BPh3 adds to the anionic Fe complex.

More specific examples include [NEt4][CpFe(CO)2] which gives the anionic borane iron complex as an amorphous solid from reaction with BPh3 in diethyl ether.

[1] In addition, there are many complex boron-centered molecules that act as multiple ligands on a single metal atom, forming "scaffolding" structures.