A family of rhodium and iridium complexes with semirigid benzylsilyl phosphines: from bidentate to tetradentate coordination modes

Abstract

The synthesis of a new trisbenzylsilanephosphine P{(o-C₆H₄CH₂)SiMe₂H}₃ (1) is shown to proceed with high yields from P(o-tolyl)₃. Compound 1 coordinates to the Rh and Ir dimers [MCl(COD)]₂ (M = Rh, Ir) in a tetradentate or tridentate fashion, depending on the strict exclusion of water. The dimeric compounds [ClM(SiMe₂CH₂-o-C₆H₄)₂P(o-C₆H₄-CH₂SiMe₂H)]₂, 2Rh and 2Ir, feature a tetradentate coordination of the starting ligand with P and two Si atoms as well as a non-classical agostic Si–H group. The presence of adventitious water in the solvents leads to the formation of two new complexes [(μ²-Cl)₂M₂(SiMe₂CH₂-o-C₆H₄)₂P(o-C₆H₄-CH₂SiMe₂OSiMe₂CH₂-o-C₆H₄–)P(SiMe₂CH₂-o-C₆H₄)₂], 3Rh and 3Ir, which feature a siloxane bridge through Si–H bond breaking in 2. Reaction of [RhCl(COD)]₂ with the bisbenzylsilanephosphine PhP{(o-C₆H₄CH₂)SiMe₂H}₂ leads to the formation of compound 4Rh which features also a dimeric structure with the SiPSi ligand coordinated through the two silicon atoms, one of which occupies the apical position of a square-pyramidal geometry in the solid state, while the second is disposed equatorially trans to π-donor Cl. Finally, bidentate coordination of a PSi ligand is achieved by reaction of [RhCl(COD)]₂ with Ph₂P{(o-C₆H₄CH₂)SiMe₂H} which leads to the monometallic species [RhCl(SiMe₂CH₂-o-C₆H₄-PPh₂)₂], 5Rh, incorporating two chelating PSi ligands and maintaining a Cl ligand.