Synthesis of a Tris(phosphaalkene)phosphine Ligand and Fundamental Organometallic Reactions on Its Sterically Shielded Metal Complexes

Abstract

A new tris(phosphaalkene)phosphine ligand ( 1 ) was synthesized via phospha-Wittig methodology. Metalation of 1 with [RhCl(C 2 H 4 ) 2 ] 2 and [IrCl(COE) 2 ] 2 (COE = cyclooctene) produced trigonal bipyramidal metal chlorides 2a (M = Rh) and 2b (M = Ir) in which the ligand coordinates in a tetradentate fashion. X-ray crystallographic studies on 1 ·1.5THF, 2a ·5CHCl 3, and 2b ·2.5CHCl 3 combined with DFT calculations revealed a pronounced change in hybridization of the phosphaalkene phosphorus atoms upon coordination to the Rh/Ir centers, resulting in highly sterically congested metal complexes. Nucleophilic substitution on 2a with NaN 3 afforded Rh–N 3 complex 3; computational analysis, IR spectroscopy, and 15 N{ 1 H} NMR spectroscopy on isotopologue 15 N-3 provided additional structural insights. Halide abstraction of the chloride in 2b with AgOTf in the presence of acetonitrile afforded cationic Ir–NCMe complex 4 . Evidence of the bound acetonitrile unit was obtained by 2D NMR spectroscopy and deuterium labeling studies.