Date: January 8, 2008
Creator: Hirsekorn, Kurt F.; Hulley, Elliott B.; Wolczanski, Peter T. & Cundari, Thomas R., 1964-
Description: This article discusses the role of density of states in second vs third row transition metal reactivity. Abstract: The substitution chemistry of olefin complexes (silox)3M(ole) (silox = tBu3SiO; M = Nb (1-ole), Ta (2-ole); ole = C2H4 (as 13C2H4 or C2D4), C2H3Me, C2H3Et, cis-2-C4H8, iso-C4H8, C2H3Ph, cC5H8, cC6H10, cC7H10 (norbornene)) was investigated. For 1-ole, substitution was dissociative (∆Gǂdiss), and in combination with calculated olefin binding free energies (∆G˚bind), activation free energies for olefin association (∆Gǂassoc) to (silox)3Nb (1) were estimated. For 2-ole, substitution was not observed prior to rearrangement to alkylidenes. Instead, activation free energies for olefin association to (silox)3Ta (2) were measured, and when combined with ∆G˚bind(calcd), estimates of olefin dissociation rates from 2-ole were obtained. Despite stronger binding energies for 1-ole vs 2-ole, the dissociation of olefins from 1-ole is much faster than that from 2-ole. The association of olefins to 1 is also much faster than that to 2. Linear free energy relationships (with respect to ∆G˚bind) characterize olefin dissociation from 1-ole, but not olefin dissociation from 2-ole, and olefin association to 2, but not olefin association to 1. Calculated transition states for olefin dissocation from (HO)3M(C2H4) (M = Nb, 1´-C2H4; Ta, 2´-C2H4) are asymmetric and have ...
Contributing Partner: UNT College of Arts and Sciences