LIGAND SUBSTITUTION AT 17-ELECTRON CENTERS - ELECTROACTIVATION OF FUNCTIONALIZED CYCLOPENTADIENYLMANGANESE TRICARBONYL COMPLEXES TO SINGLE-CO AND DOUBLE-CO SUBSTITUTION

Electrochemical oxidation of (MeCp)Mn(CO)(3) (1) in the presence of P(OEt)(3) leads to rapid single- and double-CO substitution. With analogous complexes (5-5) having bulky substituents on the cyclopentadienyl ring, the 17-electron species produced by electroactivation also undergo rapid single CO substitution, but at rates significantly reduced from that observed with 1(+); substitution of a second CO in 3(+)-5(+) is even more retarded. Digital simulations of an associative mechanism closely reproduced experimental data and allowed the reactivities of the 17-electron complexes to be quantified. The ability of bulky substituents to hinder the approach of a nucleophile to the metal was examined by determining the X-ray structure of (1,3-dimethyl-2-phenylcyclopentadienyl)Mn(CO)(3) (3): monoclinic, space group P2(1)/c, a=11.019(2) Angstrom, b=7.5631(10) Angstrom, c=17.716(2) Angstrom, beta=103.381(12)degrees, Z=4, 3273 unique reflections with I > 2 sigma(I), R=0.0376, wR2=0.0912.