Four-coordinate, trigonal pyramidal Pt(II) and Pd(II) complexes.

We report herein the characterization of electrophilic, trigonal bipyramidal {[SiP(3)(R)]Pt(L)}(+) cations ([SiP(3)(R)] = [(2-R(2)PC(6)H(4))(3)Si]; R = Ph, (i)Pr) that feature weakly coordinated ligands including CH(2)Cl(2), Et(2)O, toluene, and H(2). A cationic toluene adduct that shows a close platinum aryl C-H σ-contact is perhaps most noteworthy in this context. For the isopropyl-substituted ligand, [SiP(3)(iPr)], it has proven possible to exclude the fifth axial donor to afford the rigorously four-coordinate, trigonal pyramidal (TP) complex {[SiP(3)(iPr)]Pt}(+). An isostructural TP palladium complex {[SiP(3)(iPr)]Pd}(+) is also accessible. Prototypical four-coordinate d(8) platinum and palladium complexes are square planar. The TP d(8) cations described herein are hence geometrically distinct.