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

Abstract

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 eta2-coordinated arene complex. Two distinct transition states have been located on the potential energy surface between the eta2-coordinated arene and the oxidative addition product. The first, at relatively low energy, features an eta3-coordinated arene and connects two identical eta2-arene minima, while the second leads to cleavage of the C-X bond. The absence of intermediate C-F or C-H sigma complexes observed in other systems is traced to the ability of the 14-electron metal fragment to accommodate the eta3-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 5dpi-ppi 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.

Synthesis and Reactivity of Ru(NHC)(dppp)(CO)H2 and Ru(NHC)(dppp)(CO)HF Complexes: C–H and C–F Activation

“…Previous studies on the reactivity of partially fluorinated aromatic molecules with a wide range of transition metal complexes have revealed a wide variation of chemoselectivity. Thus, [(η 5 -C 5 Me 5 )Re(CO) 3 ], [27] [Rh(PEt 3 ) 3 H], [28] [Ir(PiPr 3 ) 2 H 5 ] [29] and [35,36] to undergo oxidative addition of either C-F or C-H bonds indicate that while C-F activation is always thermodynamically more favourable, a lower kinetic barrier usually exists for C-H cleavage.…”

Development of catalyst‐transfer condensation polymerization. Synthesis of π‐conjugated polymers with controlled molecular weight and low polydispersity

“…Accordingly, this chain-growth condensation polymerization is dependent not upon the substituent effects seen in our previous chain-growth condensation polymerization, but rather upon the unexpected ability of the Ni catalyst to migrate intramolecularly to the propagating end of the polymer molecule without diffusion to the reaction mixture. A few other reactions involving similar intramolecular transfer of metal catalysts have recently been reported, [29][30][31][32] but this was the first example of chaingrowth polymerization via intramolecular transfer of a metal catalyst. We called this type of polymerization catalyst-transfer condensation polymerization.…”

Reactions of Zirconocene Bis(trimethylsilyl)acetylene Complexes with Fluorinated Pyridines: C–H vs. C–F Bond Activation

“…[33] The activation of pentafluoropyridine in the 4-position with formation of L n M(4-C 5 NF 4 )F complexes was shown by Perutz and Braun to be typical for Ni, [44] Pd, [45] Rh [46] and Pt. [47] An example of reactions of this type is shown in Scheme 7. One can conclude from these results that the chemo-and regioselectivity of the C-H and C-F bond activations in reactions of fluorinated pyridines depends on the metals (C-F for Ti, C-H for Zr; 2-position for Ti, 4-position for Zr and Ni) and the ligands (Zr: 2-position for L = imido, 4-position for L = alkyne).…”