Recently we have prepared the novel pincer complex (N’NN’)PtMe (N’NN’ = 2,6-bis(diethylaminomethyl)-4-pyridonate), in which the N’NN’ ligand is an extremely strong p-donor to platinum; this is a π-rich analog to the previously reported π-poor (N’CN’)PtMe (N’CN’ = 2,6-bis(diethylaminomethyl)phenyl). Both N’NN’ and N’CN’ are L2X fragments. Because the π-rich nature of the N’NN’ fragment, we hypothesized that [(N’NN’)Pt]+ would far more readily add H-CH3 to form [(N’NN’)PtMeH]+ than would the [(N’NN’)Pt]+ analog. We have computationally explored the reaction coordinates of the addition/elimination reaction of methane (LANL2DZ(Pt)/6-31 G(d)(non-Pt); B3LYP) on four [L2XPt]+ fragments: [(NNN)Pt]+, [(NCN)Pt]+, [(PNP)Pt]+, and [(PCP)Pt]+ in which the NNN and NCN ligands are the dimethylaminomethyl analogs of N’NN’ and N’CN’, respectively, and the PNP and PCP ligands are the diphenylphosphinomethyl analogs. Surprisingly, in none of the four complexes was there a clear local minimum for the [L2XPtMeH]+ species, but on each intrinsic reaction coordinate the point of oxidative addition could be identified. The complexes containing pyridonate had barriers to C-H bond cleavage approximately 30 kcal/mol lower than their phenyl analogs, and the bis-phosphine and bis-amine barriers were comparable.

Preliminary computational studies of C-H reductive elimination/oxidative addition of methane with π-rich and π-poor L2XPt+ fragments

ACS Spring 2022

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