OXIDATIVE SUBSTITUTION OF MN(CO)5- BY 3,5-DI-TERT-BUTYL-1,2-BENZOQUINONE - SYNTHESIS AND CHARACTERIZATION OF THE UNSATURATED MN(CO)3(DBCAT)- ANION

Bu4N+ and PPN+ salts of the Mn(CO)3(DBCat)− anion were prepared by oxidative substitution of two CO ligands of Mn(CO)5 − by 3,5-di-tert-butyl-1,2-benzoquinone. The product was characterized by crystallography and by UV-vis, IR, 13C, and 1H NMR spectroscopy. The complex exhibits some unusual properties: (i) it is a five-coordinate, formally 16-electron, species that shows no tendency to add a sixth ligand, (ii) π-acceptor (CO) and π-donor (catecholate) ligands are combined in the coordination sphere, and (iii) intense LMCT absorption bands are observed. Strong Cat → Mn π donation seems to account for this behavior. The complex exhibits two one-electron ligand-localized oxidations at −0.03 and +0.86 V (vs Ag/AgCl) and a one-electron reduction at −1.72 V. The primary product of the first oxidation, Mn(CO)3(DBSQ), readily coordinates with a donor solvent molecule. Crystals of Bu4N+[Mn(CO)3(DBCat)] form in the triclinic space group {formula-omited} in a unit cell of dimensions a = 10.462 (2) Å, b = 21.629 (4) Å, c = 24.915 (9) Å, α = 102.61 (2)°, β = 93.19 (2)°, γ = 96.87 (2)°, and V= 5443 (2) Å3. Three crystallographically independent formula units are contained within the asymmetric region of the unit cell. None of the three independent Mn-(CO)3(DBCat)− anions have regular coordination geometries, but one has a structure that is close to trigonal bipyramidal, while the other two anions have structures that are closer to a square-pyramidal geometry. © 1990, American Chemical Society. All rights reserved.