SPANphos

Chembox new
ImageFile = SPANphos.png Section1 = Chembox Properties
Formula = C₄₇H₄₆O₂P₂
MolarMass = 704.814 g/mol

SPANphos is a diphosphine commonly used as a ligand in organometallic compounds. This compound is a rare example of a trans spanning ligand especially helpful in catalysis. By having a compound that only forms pure trans-chelating ligands, certain cis-positions will be inhibited giving way to research of new catalysts. This compound is remarkable for the fact that its trans-chelating bond is rigid in linking two trans-sites. The problem that arises from other trans-chelating compounds is that the length of the linking bond is great causing loss of rigidity, thus forming unwanted complexes such as metal to metal bonds.

ynthesis

The C2-symmetric trans-diphosphine is easily synthesized from inexpensive reagents. In the first step 4,4,4',4',6,6',-hexamethylspiro-2,2'-bichroman is prepared via an acid-catalyzed reaction between p-cresol and acetone is formed. The spirane is brominated with N-bromosuccinimide, and treated with n-BuLi and chlorodiphenylphosphine to obtain SPANphos. [cite journal | author = Z. Freixa, M. S. Beentjes, G. D. Batema, C. B. Dieleman, G. P. F. v. Strijdonck, J. N. H. Reek, P. C. J. Kamer, J. Fraanje, K. Goubitz and P. W. N. M. Van Leeuwen | title = SPANphos: A "C"₂-Symmetric "trans"-Coordinating Diphosphane Ligand | journal = Angewandte Chemie | year = 2003 | volume = 42 | issue = 11 | pages = 1322–1325 |doi = 10.1002/anie.200390330 ]

Uses

Only a few trans-chelating ligands are known, and with SPANphos there are now opportunities to discover new families of catalysts that act with ligands around the active metal center. Trans-diphosphanes, unlike cis-diphosphanes, have a chiral backbone that works with substituents on the phosphorus atom to contribute to the formation of a chiral cavity around the metal center. In Pd and Pt complexes SPANphos acts only as a trans-coordinating diphosphane ligand, giving complexes of the formula MC12(SPANphos).

References