trans-spanning ligand
Trans-spanning ligands are bidentate ligands that can span opposite sites of a complex with square-planar geometry. A wide variety of ligands that chelate in the cis fashion already exist, but very few can link opposite vertices on a coordination polyhedron. Early attempts to generate trans-spanning bidentate ligands relied on long hydrocarbon chains to link the donor functionalities, but such ligands often lead to coordination polymers.
History
A diphosphane linked with pentamethylene was claimed to span across a square planar complex. This early attempt was followed by ligands with more rigid backbones. "TRANSPHOS" was the first trans-spanning diphosphane ligand that usually coordinates to palladium(II) and platinum(II) in a trans manner. TRANSPHOS features benzo[c]phenanthrene substituted by diphenylphosphinomethyl (Ph2PCH2) groups at the 1 and 11 positions.{{cite journal | last1 = Destefano | first1 = N. J. | last2 = Johnson | first2 = D. K. | last3 = Lane | first3 = R. M. | last4 = Venanzi | first4 = L. M. | year = 1976 | title = Transition-Metal Complexes with Bidentate Ligands Spanning Trans-Positions. I. The Synthesis of 2,11-Bis(Diphenylphosphinomethyl)Benzo[C]-Phenanthrene, A Ligand Promoting the Formation of Square Planar Complexes | journal = Helvetica Chimica Acta | volume = 59 | pages = 2674–2682 | doi = 10.1002/hlca.19760590806 | issue = 8}}{{cite journal |author1=Mochida, J. A. |author2=Mattern, J. C. |author3=Bailar, J. Jr. | year = 1975 | title = Stereochemistry of Complex Inorganic Compounds. XXXV. A Complex Containing a Ligand That Spans Trans Positions | journal = J. Am. Chem. Soc. | volume = 97
| pages = 3021–3026 | doi = 10.1021/ja00844a017 | issue = 11}} The polycyclic framework suffers sterically clashing hydrogen centers.
References
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