SIGMA-ACETYLIDE COMPLEXES OF RHODIUM(I), RHODIUM(II), AND RHODIUM(III) - CORRELATION BETWEEN ELECTROCHEMICAL (E-DEGREES') AND SPECTROSCOPIC (DELTA-NU(C=C)) PARAMETERS AND D-PI (METAL)-]PI-STAR (ACETYLIDE) TRANSFER

Terminal acetylide complexes of rhodium(II) and rhodium(III) with the tripodal polyphosphine ligands N(CH2CH2PPh2)3 (NP3) and P(CH2CH2PPh2)3 (PP3) have been synthesized either by controlled-potential coulometry or by chemical oxidation of the Rh(I) neutral σ-acetylide compounds [(L)Rh(C≡CR)] (L = NP3, R = Ph, CO2Et; L = PP3, R = Ph, CO2Et, CHO). All of the compounds undergo electron-transfer reactions that encompass the Rh(I), Rh(II), and Rh(III) oxidation states of the metal. The characterization has been carried out by IR, NMR, and ESR techniques. The presence of a significant dπ (metal) → π* (acetylide) interaction in the HOMO is diagnosed by comparing and contrasting either the stretching frequencies ν(C≡C) within the members of the [(L)Rh(C≡CR)]n+ family (n =0–2) or the redox potentials E°’ within the more numerous [(L)RhX] family (X = Cl, H, C≡CR, CN, CO). © 1990, American Chemical Society. All rights reserved.