Computational studies of transition metal complexes relevant to alkane dehydrogenation, alkene oligomerization, and carbon-carbon bond formation.

摘要

Alkane dehydrogenation using coordinatively unsaturated pincer catalysts (PNP)M (PNP = kappa2-2,6-NC5H3[CH 2PMe2]2; M=Fe, Ru, Os) and (PCP)M (PCP = kappa 2-2,6-C6H3[CH2PMe2] 2; M=Co,Rh,Ir) was investigated using density functional theory (B3LYP) with a focus on kinetic and thermodynamic parameters. The free energy barriers to transfer and acceptorless dehydrogenation of propane were studied. Possible alternatives to iridium-based catalysts were found.; Select reactions were also studied for the related "POCOP" iridium catalyst, (X-POCOP)Ir (POCOP = kappa3-2,4,6-C6H2[OPR 2]2X, (X = H, MeO; R = methyl). The O atoms were found to donate electron density through the pincer ring to the metal center, and this thermodynamically favors C-H addition. The POCOP carbonyl adduct is calculated to have a CO stretching frequency lower than the analogous (MePCP)Ir-CO, in accord with experimental observations. This was shown to be due to electrostatic effects. Similar reactions were studied using "(FPCP)Ir" fluorinated species (e.g. [kappa2-2,6-C6H 3[CH2PF2]Ir).; The (MePEP)M catalysts were also studied as agents for C-C bond forming reactions. Such reactions are very attractive as "atom-economical" synthetic organic chemistry. Such reactions were also postulated for the addition of unsaturated bonds across functionalized arene C-H bonds, using a bis-phosphine non-pincer ruthenium catalyst instead of the pincer iridium.; The addition of functionalized arenes was also modeled using the pincer iridium catalyst. These products were calculated to be extremely stable six-coordinate intermediates. Studies were performed to investigate the sources of this stability.; In addition, a separate square planar P-O bidentate Ni(II) catalyst was studied. Such species serve as the basis for Shell Higher Olefin Process (SHOP) for alkene oligomerization. The asymmetry of the bidentate ligand provided two very energetically different alkene insertion pathways; this was linked to the very different trans influence of the two coordinating groups. Trans influence was found to be more dependent on atomic polarizability and less affected by the quantity of charge on the coordinating groups.