Theoretical studies of inorganic and organometallic reaction mechanisms.: 14.: -hydrogen transfer and alkene/alkyne insertion at a cationic iridium center Academic Article uri icon

abstract

  • Recent experimental work shows that alkanes can be activated by Cp*Ir(PMe3)(CH3)+ at room temperature to generate olefin complexes. The reaction begins with alkane activation by oxidative addition (OA) followed by reductive elimination (RE) of methane and then olefin formation by the -H transfer from the bound alkyl. Ab initio calculations and density functional theory (DFT) studies of ethane activation by CpIr(PH3)(CH3)+ (1) to generate CpIr-(PH3)(2-C2H4)(H) + (7) show that the -H transfer from CpIr(PH3)(C2H5)+ (5) to 7 is exothermic by 12 and 16 kcal/mol with a very low barrier of 0.7 and 0.4 kcal/mol at the DFT and CCSD levels, respectively. Thus, the rate-determining step in alkane dehydrogenation to olefin complexes by Cp*Ir(PMe3)(CH3)+ is the alkane OA step. These results are in very good agreement with the experimental work of Bergman and co-workers. A strong stabilizing interaction between either ethylene or acetylene and CpIr(PH3)(CH3)+ leads to high activation barriers (25-36 kcal/mol) for the insertion processes of ethylene or acetylene. In comparison to ethylene, the insertion reaction of acetylene with the CpIr(PH3)(CH3)+ complex is more favorable. Thus, the dimerization of terminal alkynes catalyzed by cationic iridium complexes is plausible. 1998 American Chemical Society.

published proceedings

  • ORGANOMETALLICS

author list (cited authors)

  • Niu, S. Q., Zaric, S., Bayse, C. A., Strout, D. L., & Hall, M. B.

citation count

  • 27

complete list of authors

  • Niu, SQ||Zaric, S||Bayse, CA||Strout, DL||Hall, MB

publication date

  • November 1998