Chain Length and Coordinating Properties
The short-chain diphosphine dppm tends to promote metal-metal interactions as illustrated by A-frame complexes. When the two phosphine substituents are linked by two to four carbon centres, the resulting ligands often chelate rings with a single metal. The most common diphosphine ligand is 1,2-Bis(diphenylphosphino)ethane, which forms a five-membered chelate ring with most metals.
Some diphosphines, such as the extraordinary case of tBu2P(CH2)10PtBu2, give macrocyclic complexes with as many as 72 atoms in a ring.
To position phosphine donor groups trans on a coordination sphere, several atoms are required to link the donor centres and long-chain diphosphines are typically floppy and do not chelate well. This challenge has been resolved by the long but rigid diphosphine SPANphos.
Read more about this topic: Diphosphines
Famous quotes containing the words chain, length and/or properties:
“We are all bound to the throne of the Supreme Being by a flexible chain which restrains without enslaving us. The most wonderful aspect of the universal scheme of things is the action of free beings under divine guidance.”
—Joseph De Maistre (1753–1821)
“When I had mapped the pond ... I laid a rule on the map lengthwise, and then breadthwise, and found, to my surprise, that the line of greatest length intersected the line of greatest breadth exactly at the point of greatest depth.”
—Henry David Thoreau (1817–1862)
“A drop of water has the properties of the sea, but cannot exhibit a storm. There is beauty of a concert, as well as of a flute; strength of a host, as well as of a hero.”
—Ralph Waldo Emerson (1803–1882)