A Comparison of C−F and C−H Bond Activation by Zerovalent Ni and Pt:  A Density Functional Study

• Published in: Journal of the American Chemical Society Vol. 126; no. 16; pp. 5268 - 5276
• Main Authors: Reinhold, Meike, McGrady, John E, Perutz, Robin N
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 28.04.2004
• Subjects: Chemistry; Exact sciences and technology; Kinetics and mechanisms; Organic chemistry; Reactivity and mechanisms; Platinum Complexes; Nickel Complexes; Exothermic reaction; Reaction path; Organic ligand; Theoretical study; Activation parameter; Transition metal Complexes; Fluorocarbon; Energy barrier; Chemical activation; Ditertiary phosphine; Transition state; Density functional method; Potential energy surfaces
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0396908

Density functional theory indicates that oxidative addition of the C−F and C−H bonds in C6F6 and C6H6 at zerovalent nickel and platinum fragments, M(H2PCH2CH2PH2), proceeds via initial exothermic formation of an η2-coordinated arene complex. Two distinct transition states have been located on the potential energy surface between the η2-coordinated arene and the oxidative addition product. The first, at relatively low energy, features an η3-coordinated arene and connects two identical η2-arene minima, while the second leads to cleavage of the C−X bond. The absence of intermediate C−F or C−H σ complexes observed in other systems is traced to the ability of the 14-electron metal fragment to accommodate the η3-coordination mode in the first transition state. Oxidative addition of the C−F bond is exothermic at both nickel and platinum, but the barrier is significantly higher for the heavier element as a result of strong 5dπ−pπ repulsions in the transition state. Similar repulsive interactions lead to a relatively long Pt−F bond with a lower stretching frequency in the oxidative addition product. Activation of the C−H bond is, in contrast, exothermic only for the platinum complex. We conclude that the nickel system is better suited to selective C−F bond activation than its platinum analogue for two reasons:  the strong thermodynamic preference for C−F over C−H bond activation and the relatively low kinetic barrier.