Pennington-Boggio Megan K, Conley Brian L, Richmond Michael G, Williams Travis J
Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, California 90089-1661.
Department of Chemistry, University of North Texas, Denton, Texas 76203,
Polyhedron. 2014 Dec 14;84:24-31. doi: 10.1016/j.poly.2014.05.042.
Rhodium(I) and Iridium(I) borate complexes of the structure [MeB(2-py)]ML (L = (tBuNC), (CO), (CH), 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.
制备了结构为[MeB(2 - py)]ML（L = (tBuNC)、(CO)、(CH)、环辛二烯、1,2 - 二苯基膦乙烷）的铑(I)和铱(I)硼酸盐配合物，并对其进行了结构表征（环辛二烯 = 1,5 - 环辛二烯；1,2 - 二苯基膦乙烷 = 1,2 - 二苯基膦乙烷）。每个配合物都含有一个船型构型的螯合环，该螯合环会发生船型到船型的环翻转。计算证据表明，环翻转通过一个在螯合环附近接近平面的过渡态进行。我们观察到这种环翻转的势垒与金属上辅助配体基团的π受体能力之间存在经验性的定量相关性。环翻转势垒与托尔曼和利弗配体参数化方案的相关性较弱，显然是因为这些方案同时结合了σ和π效应，而我们认为环翻转势垒主要由π键主导。这一观察结果与金属 - 配体π相互作用仅在螯合环翻转的近平面过渡态而非船型构型的基态中暂时可用相一致。因此，这是首次观察到金属 - 配体π键控制构象动力学。
