| Popis: |
Four novel rhodium dimers, [Rh2(dmb)4)(BPh4)2+ (dmb = 2,2dimethyl-1,3-diisocyanopropane), BPh4- = tetraphenyl borate), [Rh2(dmb)4Cl2]Cl2, [Rh2(dmb)4I2](PF6)2 and [Rh2(dmb)2(dppm)2](BPh4)2 (dppm = bis(diphenylphosphinomethane)) are synthesized and characterized to probe the kinetic and mechanistic behavior of a photochromic system formed when [Rh2(dmb)4]2+ is mixed with methyl viologen iodide in acetonitrile. The photochromic species is tentatively identified as a metastable tetrameric complex. An identical tetrameric species is produced during an iodine titration; the instability of the tetramer is discussed. The crystal structures of [Rh2(dmb)4](BPh4)2, [Rh2(dmb)4Cl2]Cl2 and [Rh2(dmb)2(dppm)2](BPh4)2 are presented. The oxidation reaction also yields [Rh2(dmb)4I2]2+ as a final product, in 1:1 stoichiometry. The [Rh2(dmb)2(dppm)2]2+ species does not form a tetrameric complex and is used to study the kinetics and mechanism of the oxidative-addition reaction with iodine. Ionic strength is a complicating factor to understand the kinetics of this oxidation reaction. The mechanism is not fully described by a simple two-step process, but involves complex intermediate(s). Several mechanisms are proposed and discussed.The Pt(dbbpy)(bdt) (dbbpy = 4-4’-dibutyl-2,2’-bipyridine) (bdt = 1,2-dithiolbenzene) complex is synthesized and characterized. The platinum monomer reacts with methyl iodide to yield asymmetric [Pt(dbbpy)(CH3bdt)]I, characterization data is consistent with the methylation of a single sulfur. The crystal structure of Pt(dbbpy)(bdt) and Pt(dbbpy)(bdtO2) are discussed. The kinetics of the reaction and a proposed mechanism are presented. The data agree well with similar experiments (enthalpy and entropy of activation) but there is some disagreement in the literature as to the mechanism(s) that thiol methylation exploit.The synthetic attempt of [Rh2(dmb)4Br2]Br2 and [Rh2(dmb)2(dppe)2]Cl2 (dppe = 1,2-bis(diphenylphosphinoethane)) are presented. Preliminary results of the titration of [Rh2(dmb)4]2+ with bromine and the methylation of [Rh2(dmb)2(dppm)2]2+ by CH3I are discussed. |
