C−H Activation at a Cationic Platinum (II) Center:  A Quantum Chemical Investigation

Abstract

The elementary steps of a recently reported methane activation reaction involving a platinum complex with a bidentate nitrogen ligand have been investigated using quantum chemical methods based on density functional theory. Our findings support a reaction mechanism involving formation of a σ-complex followed by oxidative addition.

The σ‐CAM Mechanism: σ Complexes as the Basis of σ‐Bond Metathesis at Late‐Transition‐Metal Centers

“…The degenerate exchange step in the methyl(h 2 -methane) ana- + cation is shown to have a much lower barrier with an oxidative cleavage mechanism than a s-bond metathesis mechanism and consequently s-CAM is excluded. [90] It is remarkable that, despite the differences between H, Si, B, and C, similar s complexes and dynamics can occur, as shown in the previous examples. The simplicity of the dihydrogen ligand contrasts with the more complex bonding of the other s ligands.…”

Der σ‐CAM‐Mechanismus: σ‐Komplexe als Schlüssel der σ‐Bindungsmetathese bei späten Übergangsmetallen

“…Diese Studie kann man den aus theoretischen Arbeiten erhaltenen Modellen des Methanaustauschs für die Umsetzung von [Pt(Me 2 NCH 2 CH 2 NMe 2 )(L)(CH 3 )] + (L=Pentafluorpyridin) mit 13 CH 4 gegenüberstellen 89. Die entartete Austauschreaktion des [Pt(CH 3 )(η 2 ‐CH 4 )] + ‐Ions hat demnach eine viel geringere Barriere für eine oxidative Spaltung als für eine σ‐Bindungsmetathese, sodass der σ‐CAM‐Mechanismus ausgeschlossen ist 90…”

Catalytic Processes Involving Dihydrogen Complexes and Other Sigma-bond Complexes

“…Also, calculations support a heterolytic mechanism in scheme 12 over one based on C-H oxidative addition [141]. However other calculations favor OA pathways in methane activation on model complexes such as M(CH 3 )(HN=CHCH=NH) (M=Pd + , Pt + , Rh + , Ir + , Rh, Ir), the exceptions being Pd + and Rh + [145]. Thus for third-row metal centers, even if they are electrophilic, the two pathways are close in energy (and may even occur concurrently [135]), depending on factors such as ancillary ligand properties and reaction conditions.…”