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

A new
tris­(phosphaalkene)­phosphine ligand (1) was
synthesized via phospha-Wittig methodology. Metalation of 1 with [RhCl­(C2H4)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·5CHCl3, and 2b·2.5CHCl3 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 NaN3 afforded Rh–N3 complex 3;
computational analysis, IR spectroscopy, and 15N­{1H} NMR spectroscopy on isotopologue 15N-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.