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

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.