title: Synthesis, Structure, and Conformational Dynamics of Rhodium and Iridium Complexes of Dimethylbis(2-pyridyl)borate.
abstract: Rhodium(I) and Iridium(I) borate complexes of the structure [Me2B(2-py)2]ML2(L2= (tBuNC)2, (CO)2, (C2H4)2, cod, dppe) were prepared and structurally characterized (cod = 1,5-cyclooctadiene; dppe = 1,2-diphenylphosphinoethane). Each contains a boat-configured chelate ring that participates in a boat-to-boat ring flip. Computational evidence shows that the ring flip proceeds through a transition state that is near planarity about the chelate ring. We observe an empirical, quantitative correlation between the barrier of this ring flip and the π acceptor ability of the ancillary ligand groups on the metal. The ring flip barrier correlates weakly to the Tolman and Lever ligand parameterization schemes, apparently because these combine both σ and π effects while we propose that the ring flip barrier is dominated by π bonding. This observation is consistent with metal-ligand π interactions becoming temporarily available only in the near-planar transition state of the chelate ring flip and not the boat-configured ground state. Thus, this is a first-of-class observation of metal-ligand π bonding governing conformational dynamics.
authors.affiliation: Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, California 90089-1661.
authors.forename: Megan K
authors.initials: MK
authors.lastname: Pennington-Boggio
authors.affiliation: Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, California 90089-1661.
authors.forename: Brian L
authors.initials: BL
authors.lastname: Conley
authors.affiliation: Department of Chemistry, University of North Texas, Denton, Texas 76203, cobalt@unt.edu.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Richmond
authors.affiliation: Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, California 90089-1661.
authors.forename: Travis J
authors.initials: TJ
authors.lastname: Williams
keywords: Back Bonding; Inversion Recovery; Iridium; Rhodium; Ring Flip