Synthesis, Structure, and Properties of 9-Phospha-10-silatriptycenes and their Derivatives

A variety of 9-phospha-10-silatriptycenes (PSiT) and some derivatives, such as the phosphine selenides
and cis-platinum complexes, have been prepared in order to study their structures and characteristics as
a phosphine ligand. The 1J(P−Se) NMR coupling constant of the phosphine selenides demonstrate the
large s character of the lone pair orbital on the phosphorus atom, attributable to the small C−P−C bond
angles of the PSiT framework, as confirmed by X-ray crystallography. The strong trans influence of
PSiT has been determined from the 1J(Pt−C) coupling constant measurements of the cis-[PtMe2(psit)2],
which is due to the increase in the P−Pt−P angle in the complexes derived from the steric repulsion
between the two bulky PSiT ligands. Both the substituent on the silicon and the bridging benzene rings
affect the electronic character. Electron-withdrawing substituents on the silicon atom slightly increase
the s character of the phosphorus lone pair orbital, and the isopropoxy groups on the bridging benzene
rings increase the trans influence.