Date: March 15, 2003
Creator: Cooney, Katharine D.; Cundari, Thomas R., 1964-; Hoffman, Norris W.; Pittard, Karl A.; Temple, M. Danielle & Zhao, Yong
Description: This article discusses research that has demonstrated the utility of a rigorously calibrated, molecular mechanics/semiempirical quantum mechanical protocol for developing stereoelectronic (Tolman) maps for phosphine ligands. A computational analysis of alkyl and aryl phosphines in common usage suggests that these ligands are quite similar stereoelectronically. A noticeable gap int he Tolman map for common phosphines is observed for large, electron-poor phosphines. Several candidates meeting these criteria were identified, the most promising of which is P(t-C₄F₉)₃. Phosphines in which the phosphorus participates in a ring, which comprise a very small subset of reported phosphines, have very interesting stereoelectronic properties, particularly those in which the ligating phosphorus is part of a three-membered ring. In terms of steric properties, the symmetric deformation coordinate proposed by Orpen and co-workers on the basis of crystallographic studies is calculated with sufficient accuracy using PM3(tm) to allow good confidence in predictions of novel phosphines. For quantification of the electronic properties of phosphines, the authors analyzed changes in the CO stretching frequency upon changing the ancillary phosphine ligands.
Contributing Partner: UNT College of Arts and Sciences